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 summary is based on a systematic review that 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. [This summary is based on Bondebjerg, A., Dalgaard, N. T., Filges, T., & Viinholt, B. C. A. (2023). The effects of small class sizes on students' academic achievement, socioemotional development and well-being in special education: A systematic review. Campbell Systematic Reviews, 19, e1345. https://doi.org/10.1002/cl2.1345.]