Does class size have an effect, we know it does but that it’s a bit more complicated than that, check here but do notice that e.g. Hattie shows a relatively small effect size. School size has been proven a bigger effect, but still you often hear pleas for bigger schools.
It’s an ongoing debate which always can benefit from nuance, and this study by Gershenson & Langbein I found via Best Evidence in Brief adds nuance.
A new article in Educational Evaluation and Policy Analysis looks at primary school size and academic performance, and concludes that for most students there is no causal relationship.
The authors used administrative records on 691,450 students aged 8-11 who attended 1,417 schools in North Carolina between 2004 and 2010. The data contained end-of-year math and reading scores, student demographics, classroom identifiers, and a set of school-level characteristics including total enrollment, average daily attendance, suspensions, expulsions, crimes per 1,000 students, and geographic locale.
The primary analysis provided no evidence of a causal relationship between school size and overall student achievement, regardless of whether school size was measured at the school or grade level.
However, two subgroups were significantly harmed by increases in school size. The math and reading achievement of students with special educational needs (SEN) was lower in large schools, as was the reading achievement (but not math) of socioeconomically disadvantaged students. The authors suggest that SEN students may be particularly sensitive to increases in school size either because larger schools are less able to match their needs to relevant support programs, or because they are more sensitive to the weaker social bonds that may be inherent in larger schools. The authors also cite previous research that suggests that disadvantaged students who receive less attention at home may benefit from the greater individual attention provided by smaller schools.
Abstract from the study:
Evidence on optimal school size is mixed. We estimate the effect of transitory changes in school size on the academic achievement of fourth- and fifth-grade students in North Carolina using student-level longitudinal administrative data. Estimates of value-added models that condition on school-specific linear time trends and a variety of teacher-by-school, student, and school-by-year fixed effects suggest that, on average, there is no causal relationship between school size and academic performance. However, two subgroups of interest are significantly harmed by school size: socioeconomically disadvantaged students and students with learning disabilities. The largest effects are observed among students with learning disabilities: A 10-student increase in grade size is found to decrease their math and reading achievement by about 0.015 test-score standard deviations.