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Class size reductions in general education are some of the most researched educational interventions in social science, yet researchers have not reached any final conclusions regarding their effects. While research on the relationship between general education class size and student achievement is plentiful, research on class size in special education is scarce, even though class size issues must be considered particularly important to students with special educational needs. These students compose a highly diverse group in terms of diagnoses, functional levels, and support needs, but they share a common need for special educational accommodations, which often entails additional instructional support in smaller units than what is normally provided in general education. At this point, there is however a lack of clarity as to the effects of special education class sizes on student academic achievement and socioemotional development. Inevitably, such lack of clarity is an obstacle for special educators and policymakers trying to make informed decisions. This highlights the policy relevance of the current systematic review, in which we sought to examine the effects of small class sizes in special education on the academic achievement, socioemotional development, and well‐being of children with special educational needs.
The objective of this systematic review was to uncover and synthesise data from studies to assess the impact of small class sizes on the academic achievement, socioemotional development, and well‐being of students with special educational needs. We also aimed to investigate the extent to which the effects differed among subgroups of students. Finally, we planned to perform a qualitative exploration of the experiences of children, teachers, and parents with class size issues in special education.
Relevant studies were identified through electronic searches in bibliographic databases, searches in grey literature resources, searches using Internet search engines, hand‐searches of specific targeted journals, and citation‐tracking. The following bibliographic databases were searched in April 2021: ERIC (EBSCO‐host), Academic Search Premier (EBSCO‐host), EconLit (EBSCO‐host), APA PsycINFO (EBSCO‐host), SocINDEX (EBSCO‐host), International Bibliography of the Social Sciences (ProQuest), Sociological Abstracts (ProQuest), and Web of Science (Clarivate, Science Citation Index Expanded & Social Sciences Citation Index). EBSCO OPEN Dissertations was also searched in April 2021, while the remaining searches for grey literature, hand‐searches in key journals, and citation‐tracking took place between January and May 2022.
The intervention in this review was a small special education class size. Eligible quantitative study designs were studies that used a well‐defined control or comparison group, that is, studies where there was a comparison between students in smaller classes and students in larger classes. Children with special educational needs in grades K‐12 (or the equivalent in European countries) in special education were eligible. In addition to exploring the effects of small class sizes in special education from a quantitative perspective, we aimed to gain insight into the lived experiences of children, teachers, and parents with class size issues in special education contexts, as they are presented in the qualitative research literature. The review therefore also included all types of empirical qualitative studies that collected primary data and provided descriptions of main methodological issues such as selection of informants, data collection procedures, and type of data analysis. Eligible qualitative study designs included but were not limited to studies using ethnographic observation or field work formats, or qualitative interview techniques applied to individual or focus group conversations.
The literature search yielded a total of 26,141 records which were screened for eligibility based on title and abstract. From these, 262 potentially relevant records were retrieved and screened in full text, resulting in seven studies being included: three quantitative and five qualitative studies (one study contained both eligible quantitative and qualitative data). Two of the quantitative studies could not be used in the data synthesis as they were judged to have a critical risk of bias and, in accordance with the protocol, were excluded from the meta‐analysis on the basis that they would be more likely to mislead than inform. The third quantitative study did not provide enough information enabling us to calculate an effect size and standard error. Meta‐analysis was therefore not possible. Following quality appraisal of the qualitative studies, three qualitative studies were judged to be of sufficient methodological quality. It was not possible to perform a qualitative thematic synthesis since in two of these studies, findings particular to special education class size were scarce. Therefore, only descriptive data extraction could be performed.
Despite the comprehensive searches, the present review only included seven studies published between 1926 and 2020. Two studies were purely quantitative (Forness, 1985; Metzner, 1926) and from the U.S. Four studies used qualitative methodology (Gottlieb, 1997; Huang, 2020; Keith, 1993; Prunty, 2012) and were from the US (2), China (1), and Ireland (1). One study, MAGI Educational Services (1995), contained both eligible quantitative and qualitative data and was from the U.S.
The major finding of the present review was that there were virtually no contemporary quantitative studies exploring the effects of small class sizes in special education, thus making it impossible to perform a meta‐analysis. More research is therefore thoroughly needed. Findings from the summary of included qualitative studies reflected that to the special education students and staff members participating in these studies, smaller class sizes were the preferred option because they allowed for more individualised instruction time and increased teacher attention to students' diverse needs. It should be noted that these studies were few in number and took place in very diverse contexts and across a large time span. There is a need for more qualitative research into the views and experiences of teachers, parents, and school administrators with special education class sizes in different local contexts and across various provision models. But most importantly, future research should strive to represent the voices of children and young people with special needs since they are the experts when it comes to matters concerning their own lives.
Despite carrying out extensive literature searches, the authors of this review found only seven studies exploring the question of class size in special education. The authors therefore call for more research from quantitative and qualitative researchers alike, such that practitioners and administrators may find guidance in their endeavours to create the best possible school provisions for all children with special educational needs.
While research on the relationship between general education class size and student achievement is plentiful, research on class size in special education is scarce, even though class size issues must be considered particularly important to students with special educational needs. This systematic review sought to examine the effects of small class sizes in special education on the academic achievement, socioemotional development and well‐being of children with special educational needs.
Furthermore, the review aimed to perform a qualitative exploration of the views of children, teachers and parents concerning class size conditions in special education.
A secondary objective was to explore how potential moderators (e.g. performance at baseline, age, and type of special educational need) affected the outcomes.
What is the aim of this review?
The objective of this Campbell systematic review was to synthesise data from existing studies to assess the impact of small class sizes in special education on students' academic achievement, socioemotional outcomes and well‐being.
This review included seven studies, of which two were quantitative, four were qualitative, and one was both quantitative and qualitative. It was not possible to perform a meta‐analysis, nor a qualitative thematic synthesis. The included studies were critically assessed, coded for descriptive data, and narratively summarised.
One quantitative study was assessed to be of sufficient methodological quality following risk of bias assessment. Unfortunately, it was not possible to extract an effect size from this study since it did not report the required information and the study authors could not be contacted.
Three qualitative studies were assessed to be of sufficient methodological quality following qualitative critical appraisal.
There are surprisingly few studies exploring the effects of small class sizes in special education on any outcomes. The included qualitative studies find that smaller class sizes are the most preferred option among students with special educational needs, their teachers and school principals. This is because of the possibilities afforded in terms of individualised instruction time and increased teacher attention to the needs of each student.
The impact of small class sizes in special education is under‐researched both within the quantitative and the qualitative literature.
Future research should aim to fill this knowledge gap from diverse methodological perspectives, paying close attention to the views of parents, teachers, administrators and, most importantly, the children and young people whose everyday lives are spent in the various special education provisions.
Searches in bibliographic databases and EBSCO OPEN Dissertations were performed in April 2021, while the remaining searches for grey literature, hand searches in key journals, and citation tracking took place between January and May 2022.
Class size reductions in general education are some of the most researched educational interventions in social science, yet researchers have not reached any final conclusions regarding their effects. While some researchers point to small and insignificant differences between varying class sizes, others find positive and significant effects of small class sizes on, for example, children's academic outcomes. In a previous Campbell Systematic Review on small class sizes in general education, Filges (2018) found evidence suggesting, at best, a small effect on reading achievement, whereas there was a negative, but statistically insignificant, effect on mathematics.
While research on the relationship between general education class size and student achievement is plentiful, research on class size in special education is scarce (see e.g., McCrea, 1996; Russ, 2001; Zarghami, 2004), even though class size issues must be considered particularly important to students with special educational needs. These students compose a highly diverse group, but they share a common need for special educational accommodations, which often entails additional instructional support in smaller units than what is usually provided in general education. Special education class sizes may vary greatly, both across countries and regions, as well as across different student groups, but will usually be small relative to general education classrooms. In most cases, placement in special education, as opposed to, for example, inclusion in general education, is based exactly on the child's need for close adult support in a smaller unit, where instruction can be tailored to the needs of each child and a calmer, more structured environment can be created. Following this, one may assume that there are advantages to small class sizes in special education, in that children are placed in a suitable environment with the support they need to thrive and learn (for a discussion of perceptions on the benefits of special education, see e.g., Kavale, 2000). However, there may also be challenges to small class sizes, for example, in terms of the opportunities available for building friendships.
It should be noted that class size in special education is connected to other structural factors such as, for example, student–teacher ratio and type of special education provision. In this review, we focus on class size since our main interest lies in exploring the specific mechanisms behind being in a smaller group. However, we have paid close attention to the relatedness and potential overlap between class size and concepts such as student/teacher ratio or caseload (for more about these concepts, see Description of the intervention). When it comes to the type of special education provision, we have included all types of settings where children with special educational needs are grouped together for instruction (i.e., segregated schools/classes/groups/units to which only students with special educational needs attend).
Finally, class size issues, both in general and in special education, are associated with ongoing discussions on educational spending and budgetary constraints. Hence, in school systems imposed with financial constraints, small class sizes in special education settings may be deemed too expensive. As a result, children with special educational needs may be placed in larger units with potential adverse effects on their learning and well‐being. At this point, there is however a lack of clarity as to the effects of small class sizes in special education on student academic achievement, socioemotional development, and well‐being. Inevitably, such lack of clarity is an obstacle for special educators and policymakers trying to make informed decisions. This highlights the policy relevance of the current systematic review, in which we examined the effects of small class sizes in special education on the academic achievement, socioemotional development, and well‐being of children with special educational needs. In working towards this aim, we planned to apply an approach consisting of both a statistical meta‐analysis (if possible from the studies found through our searches) and an exploration of the experiences of children, teachers, and parents with class size issues in special education, as reported in qualitative studies. We chose to include studies applying a qualitative methodology because the combination of quantitative and qualitative methods had the potential to provide a deeper insight into the complexity of class size questions in special education, including the voices of children and teachers who spend their everyday lives in special education contexts.
Special education in this review refers to educational settings designed to provide instruction exclusively for children with special educational needs. In such settings, both the instructional and physical classroom environment may be adjusted to accommodate the specific needs of the student group, as in the use of individual work tables and visual aids (pictograms) for children on the autism spectrum. We have included studies of all kinds of special education settings that are attended only by children with special educational needs (i.e., segregated special education settings as opposed to inclusion settings where children with and without special educational needs are taught together). We have included both part‐ and full‐time special education provisions (with an example of a part‐time provision being resource rooms attended by students with specific learning difficulties within one or more academic subjects). Furthermore, no limits have been imposed concerning the placement of special education provisions, that is, we have included both separate special schools and special education classes, units or resource rooms lodged within mainstream schools. We acknowledge that significant variations exist in special education provisions across time (e.g., due to new developments in pedagogical approaches and learning aids) and between (as well as within) countries, just as we are aware of the diversity between special education provisions, for example, in terms of how they are staffed and to which degree they are specialised to work with particular student groups. Our approach has therefore been to be inclusive in our search and screening process by not imposing limits on publication date or study location and by defining special education as all kinds of provisions where children with any type of special educational need are grouped together for instruction for any given amount of time (for our definition of what constitutes a special educational need, see Types of participants).
In this review, it is important to distinguish between the following terms: class size, student–teacher ratio, and caseload. Class size refers to the number of students present in a classroom at a given point in time. Student–teacher ratio refers to the number of students per teacher within a classroom or an educational setting. Furthermore, some studies may apply the term caseload which is typically defined as the number of students with individual education plans (IEPs) for whom a teacher serves as ‘case manager’ (Minnesota Department, 2000). In this review, the intervention is a small class size. Thus, studies only considering student–teacher ratios or caseloads are not eligible.
Our rationale for focusing on class size is based in the belief that although class size and student–teacher ratios or caseloads in special education are related, they involve somewhat different assumptions about how a small class size as opposed to a larger one might change the opportunities for students and teachers. With class size, the mechanism in play is based on assumptions about the dynamics of a smaller group and the belief that with smaller groups, teachers are better able to develop an in‐depth understanding of student needs through more focused interactions, better assessment, and fewer disciplinary problems (Ehrenberg, 2001; Filges, 2018). The size of the group in itself will often be of specific importance to students with special educational needs, for example, students diagnosed with sensory processing disorders, making them sensitive to noise and movement, or students with ASD who struggle with reading social cues in larger groups. For such students, being in a larger class would likely feel overwhelming and stressful, no matter the student–teacher ratio.
Student–teacher ratio and caseload are also of great importance, but do not take in the specific mechanisms of being in a smaller group which we find to be central in special education. We acknowledge the relatedness of these concepts to class size and are aware that terms may in some cases overlap. We paid attention to this when searching for studies by adding a search term for student–teacher ratio and when screening the studies.
It is possible that the intensity of the intervention, that is, the size of a change in class size and the initial class size from which this change is made, can play a role in determining the intervention effect. For intensity, the question is: how small does a class have to be to optimise the advantage? In general education for example, large gains are attainable when class size is below 20 students (Biddle, 2002; Finn, 2002), but gains are also attainable if class size is not below 20 students (Angrist, 1999; Borland, 2005; Fredriksson, 2013; Schanzenbach, 2007). It has been argued that the impact of class size reductions of different sizes and from different baseline class sizes is reasonably stable and more or less linear when measured per student (Angrist, 2009; Schanzenbach, 2007). Other researchers argue that the effect of class size is not only non‐linear but also non‐monotonic, implying that an optimal class size exists (Borland, 2005). Thus, the question of whether the size of a change in class size and the initial class size from which the change is made matters for the magnitude of intervention effects is still an open question. For this reason, we planned to include intensity (size of change in special education class size and initial class size) as a moderator if it was possible given the information presented in the included studies.
Due to the specialised and varied nature of special needs provision, issues of class size in this area are likely to be complex (Ahearn, 1995). However, small class sizes may promote student engagement and instructional individualisation, which is of particular importance to students with special educational needs. A research report from 1997 evaluating increases in resource room instructional group size in New York City public schools may serve to illustrate the importance of individualisation in special education (Gottlieb, 1997). The report indicated that increases in instructional group sizes from 5 to at most 8 students per teacher led to decreases in the reading achievement scores of resource room students. Resource room teachers reported diminished opportunities for sufficiently helping students. Furthermore, observations revealed little time spent on individual instruction.
Small class sizes may be better suited to address the potential physical and psychological challenges of students with special educational needs, for example, by providing closer adult‐child interaction, better accommodation of individual needs, and a more focused social interaction with fewer peers. Thus, smaller class sizes in special education may have a positive impact on both academic achievement and socioemotional development as well as on student well‐being at school.
On the other hand, small class sizes may limit the possibilities for finding compatible peers with whom to build friendships, hence leading to adverse effects on student's social and personal well‐being at school. This may also impact on the options available for building social skills, which are vital to, for example, students with autism‐spectrum‐disorders. Furthermore, small class sizes may lead to decreased variation in academic and social skills within the class, limiting the potential for positive peer effects on student academic learning and socioemotional development (e.g., learning from peers with more advanced academic skills).
As reflected in the above discussion about the potential benefits (or lack thereof) pertaining to smaller class sizes in special education, the effects of any given change in class size may occur both within the realm of academic achievement as well as across socioemotional domains (covering children's psychological, emotional, and social adjustment, as well as mental health) and in terms of student well‐being (defined as children's subjective quality of life, pleasant emotions, happiness, and low levels of stress and negative moods); each of these domains (academic achievement, socioemotional development, and well‐being) are therefore included as key outcomes in the present review.
As previously noted, there is a lack of clarity as to the impact of small class sizes in special education on student academic achievement, socioemotional development, and well‐being, making it difficult for special educators and policymakers to make informed decisions. Furthermore, class size alterations are associated with ongoing discussions on educational spending and budgetary constraints, highlighting the policy relevance of strengthening the knowledge base through a systematic review of the available literature.
Few authors have tried to review the available literature on special education class sizes, and these reviews have not followed rigorous, systematic frameworks, such as that applied in a Campbell systematic review. McCrea (1996) conducted a review on special education and class size including a sample of American studies. These studies pointed to some effects of class size on the learning environment in class as well as on student achievement and behaviour, especially at the elementary level. Furthermore, in an article exploring the class size literature, Zarghami (2004) examined the effects of appropriate class size and caseload on special education student academic achievement. The authors were not able to identify a single best way to determine appropriate class and group sizes for special education instruction. However, they pointed to the existence of well‐qualified teachers as an important factor in increasing student achievement. Finally, Ahearn (1995) analysed state special education regulations on class size/caseload in the U.S. and reviewed research on class size in general education and special education. The report showed that state requirements for class size/caseload in special education programmes were much more specific and complicated than those for general education, and that the specialised nature and variety of the services delivered to students with special educational needs, combined with the restrictions attributable to specific student disabilities, contributed to those complications. In line with the article by Zarghami (2004), Ahearn (1995) concluded that there was no single best way to determine class sizes for special education programmes, adding that the information available was inadequate.
The above mentioned reviews did not apply the extensive, systematic literature searches and critical appraisals that are performed in a Campbell systematic review. Furthermore, they date back 15 years or more, which means that they do not include newer developments in special education research. Therefore, we find that the present review fills a research gap by providing an up‐to‐date overview of what (little) research is available exploring the effects of small class sizes in special education and the views of children, parents, and teachers who experience different issues related to special education class size. In this sense, the main contribution of the review lies in shedding light on the fact that more research is still needed to gain knowledge into the complexities of class size in special education.
The objective of this systematic review was to uncover and synthesise data from studies to assess the impact of small class sizes on the academic achievement, socioemotional development, and well‐being of students in special education. We also aimed to investigate the extent to which the effects differed among subgroups of students. Furthermore, we aimed to perform a qualitative exploration of the experiences of children, teachers, and parents with class size issues in special education.
The screening of potentially eligible studies for this review was performed according to inclusion criteria related to types of study designs, types of participants, types of interventions, and types of outcome measures, all of which are described in the following sections (for the screening guide, see Supporting Information: Appendix 2). These criteria were also specified in the published protocol (Bondebjerg, 2021).
To summarise what is known about the possible causal effects of small special education class sizes, we included all quantitative study designs that used a well‐defined control or comparison group, that is, studies that compared outcomes for groups of students in smaller versus larger special education classes. This is further outlined in the section Assessment of risk of bias in included studies, and the methodological appropriateness of the included quantitative studies was assessed according to the risk of bias.
The quantitative study designs included in the review were:
Randomised and quasi‐randomised controlled trials (allocated at either the individual or cluster level, for example, class/school/geographical area etc.),
Non‐randomised studies (where allocation had occurred in the course of usual decisions, was not controlled by the researcher, and included a comparison of two or more groups of participants, that is, at least a treated group and a control group).
For non‐randomised studies, where the change in class size occurred in the course of usual decisions (e.g., due to policies mandating class size alterations), we assessed whether the authors demonstrated sufficient pre‐reatment group equivalence on key participant characteristics.
Studies using single group pre‐post comparisons were not included. Non‐randomised studies using an instrumental variable approach were also not included—see Supporting Information: Appendix 1 (Justification of exclusion of studies using an instrumental variable (IV) approach) for our rationale for excluding studies of these designs. A further requirement to all types of studies (randomised as well as non‐randomised) was that they were able to identify an intervention effect. Studies where, for example, small classes were present in one school only and the comparison group was larger classes at another school (or more schools for that matter), would not be able to separate the treatment effect from the school effect.
The treatment in this review was a small class size. To investigate the effects of small class sizes, we included studies that compared students in smaller classes with students in larger classes. This meant that we included both studies where the intervention consisted of a reduction in class size and studies where there was an increase in class size, since both types of studies (if robustly conducted) would allow us to compare the outcomes of children in smaller classes with those of children in larger classes. We only included studies that used measures of class size and measures of outcome data at the individual or class level. We excluded studies that relied on measures of class size and measures of outcomes aggregated to a level higher than the class (e.g., school or school district).
In addition to exploring the causal effects of small class sizes in special education through an analysis of quantitative studies meeting the criteria above, we aimed to gain qualitative insight into the experiences of children, teachers, and parents with class size issues in special education contexts. To this end, we included all types of empirical qualitative studies that collected primary data and provided descriptions of main methodological issues such as informant selection, data collection procedures, and type of data analysis. Eligible qualitative studies may apply a wealth of data collection methods, including (but not limited) to participant observations, in‐depth interviews, or focus groups.
If we found mixed‐methods studies combining qualitative and quantitative data collection procedures, we assessed whether the quantitative data were eligible for inclusion in the quantitative part of the review (i.e., the quantitative data met the criteria imposed on studies exploring causal relationships), and whether the qualitative data met the criteria imposed on qualitative studies. If a study contained both eligible quantitative and qualitative data, it was included for both quantitative and qualitative quality assessment and data extraction and was counted in both categories. If there were only eligible quantitative data, the study was included only in the quantitative part of the review, and vice‐versa for qualitative studies. That is, mixed methods studies were not treated as a separate category, but were included if either their quantitative or their qualitative research components met the inclusion criteria for quantitative or qualitative studies, respectively.
The review included studies of children with special educational needs in grades K‐12 (or the equivalent in European countries) in special education. Studies that met the inclusion criteria were accepted from all countries. In this review, we excluded children in home‐ or preschool as well as children placed in treatment facilities.
Some controversy exists regarding the definition of what constitutes a special educational need (Vehmas, 2010; Wilson, 2002). In this review, we were guided by the definition from the US Individuals with Disabilities Education Act (IDEA), in which special needs are divided into 13 different disability categories 1 :
specific learning disability (covers challenges related to a child's ability to read, write, listen, speak or do math, e.g., dyslexia or dyscalculia),
other health impairment (covers conditions limiting a child's strength, energy, or alertness, e.g., ADHD),
autism spectrum disorder (ASD), emotional disturbance (may include e.g., anxiety, obsessive‐compulsive disorder and depression),speech or language impairment (covers difficulties with speech or language, e.g., language problems affecting a child's ability to understand words or express herself),
visual impairment (covers eyesight problems, including partial sight and blindness), deafness (covers instances where a child cannot hear most or all sounds, even with a hearing aid), hearing impairment (refers to a hearing loss not covered by the definition of deafness), deaf‐blindness (covers children suffering from both severe hearing and vision loss),orthopaedic impairment (covers instances when a child has problems with bodily function or ability, as in the case of cerebral palsy),
intellectual disability (covers below‐average intellectual ability), traumatic brain injury (covers brain injuries caused by accidents or other kinds of physical force), multiple disabilities (children with more than one condition covered by the IDEA criteria).While the above listed criteria provided useful guidance, we were fully aware that they should not be conceived as exhaustive, nor as clear‐cut definitions of what constitutes special educational needs. Therefore, we did not restrict ourselves to only include studies that defined their participants with these terms or which provided detailed information about types of special educational needs. Rather, we included all studies where the participating students received instruction in segregated special education settings (since we took placement in such settings to necessarily indicate a need for specialised educational support) and planned to explore the potential variation between different groups of students, if possible from the included studies.
In this review, we were interested in investigating whether small class sizes in special education resulted in better academic achievement, socioemotional development, and well‐being for students in special education when compared to larger class sizes. To answer this question, we included studies where special education class size was altered either as a result of a deliberate experiment (where class size was directly manipulated by researchers) or as a result of a naturally occurring change in class size arising due to, for example, the implementation of a new class size policy. This meant that the intervention of interest to this review was a change in special education class size allowing for a comparison between students in smaller classes versus students in larger classes. That is, the question of the effect of small class sizes could be investigated both by looking at studies where class size was reduced and where class size was increased, provided that the studies used a control or comparison group of students in smaller or larger special education classes than the treated group.
The more precisely a class size is measured, the more reliable the findings of a study will be. Studies only considering the average class size measured as student–teacher ratio within a school (or at higher levels) were not eligible. Studies where the intervention was the assignment of an extra teacher (or teaching assistants or other adults) to a class were not eligible. The assignment of additional teachers (or teaching assistants or other adults) to a classroom is not the same as changing the size of the class, and this review focused exclusively on class size. We acknowledged that class size can change per subject or eventually vary during the day, which is why the precision of the class size measure was recorded if possible.
Special education refers to settings where children with special educational needs are taught in classes segregated from general education students. These classes may be composed of children with similar special educational needs (such as classes specifically for children with ASD) or they may consist of mixed groups of children with diverse special educational needs. In such settings, the instructional environment is adjusted to accommodate the specific needs of the student group. In the present review, special education was thus defined as any given group composition consisting of only children with special educational needs. In some studies, special education was also referred to as, for example, segregated placement or resource room. Special education could be full‐time or part‐time (e.g., in the form of resource rooms attended by students for parts of the day). We included studies of all kinds of special education.
For quantitative studies, only valid and reliable outcomes that had been used on different populations were eligible.
Academic achievement (measured with e.g., the Woodcock‐Johnson III Tests of Achievement, Mather, 2001), socioemotional development and adjustment (measured with e.g., The Strengths and Difficulties Questionnaire [SDQ], Goodman, 2001), and well‐being (measured with e.g. The Perceived Competence Scale for Children, Harter, 1982) were categorised as primary outcomes.
In addition to the primary outcomes, we considered school completion rates as a secondary outcome. Furthermore, we included validated measures of student classroom behaviour, such as structured observations of student engagement, on‐task behaviour, and disruptive behaviour (measured with e.g., The Code for Instructional Structure and Student Academic Response [CISSAR], Greenwood, 1978).
Studies were only included if they considered at least one of the primary or secondary outcomes.
The review aimed to include follow‐up measures at any given point if meaningful based on the objectives for the review. However, none of the included studies reported outcomes past the end of the intervention.
For the qualitative analysis, we were interested in exploring the experiences of children, teachers, and parents with special education class sizes, as they presented themselves through, for example, in‐depth qualitative interviews or participant observations. Relevant data could stem from, for example, interviews with teachers on their perceptions of childrens' academic achievement and well‐being in small versus large special education classes, or their experiences with ensuring student engagement and attention under different class sizes. We did not define a list of outcomes in advance, but remained open to what presented itself as important to children, teachers, and parents concerning special education class sizes.
In this review, we included studies of children with special educational needs placed in any special education setting. We excluded studies of children in home‐ or preschool as well as children placed in treatment facilities.
Relevant quantitative and qualitative studies were identified through searches in electronic databases, grey literature resources, and Internet search engines, as well as through hand‐searches in specific targeted journals and citation‐tracking. We searched for both published and unpublished literature and screened references in English, Danish, Swedish, and Norwegian.
Locating qualitative research presents the reviewer with particular challenges since existing search strategies have largely been developed for and applied to the quantitative literature (Frandsen, 2016). As of yet, not all databases have implemented rich qualitative vocabularies or specific structures tailored to accommodate qualitative literature searches. Furthermore, screening on title and abstract may prove challenging since titles and abstracts in qualitative studies are sometimes more focused on content than on issues of methodology (Ibid). Attempts have been made to develop tools specifically designed for qualitative literature searches as an answer to the perceived difficulties in using such existing tools as the PICO(s) framework (Population, Intervention, Comparison (or control), Outcome, and Study design and type). Cooke (2012), for example, present the SPIDER search strategy which attempts to adapt the PICO components to make them more suitable for qualitative research. The SPIDER strategy contains the following components: Sample, Phenomenon of Interest, Design, Evaluation, and Research type. In the study by Cooke (2012), two systematic searches are performed, using first the PICO framework and then the SPIDER tool. The results show that the PICO search strategy generates a large number of hits, while the SPIDER tool leads to fewer hits, with the potential advantage of greater specificity. This means that the SPIDER tool may be more precise and easier to manage in terms of the amount of references for screening, however carrying the risk of missing studies.
In this review, we applied elements of the PICO(s) framework to search for both quantitative and qualitative studies by adding both quantitative and qualitative methodological terms in the search string, as well as by carefully looking for both types of studies in our grey literature and hand‐searches. By choosing this strategy, we prioritised the breadth and comprehensiveness of our search (sensitivity) which seemed the most appropriate choice given the anticipated low number of studies exploring class size effects particular to special education. Given the low number of studies found in the searches, we are convinced that our comprehensive approach was the best choice for this particular review topic.
The following bibliographic databases were searched in April 2021: