Education Research

Meta-Analysis: Class Size Doesn't Really Matter

• By Dian Schaffhauser
• 11/26/18

A survey of research on the impact of small class sizes found evidence that "suggests at best a small effect on reading achievement" and "a negative, but statistically insignificant, effect on mathematics."

The research was undertaken by three people at the Danish Center for Social Science Research and published by Norway-based Campbell Collaboration. The project initially began with findings from 127 relevant studies produced in 41 countries that measured the effects of class size on academic achievement up to February 2017; that was eventually winnowed down to just 10 studies for a meta-analysis.

As a report on the findings noted, reducing class size is "costly" and may even be "counterproductive" for some students. It's an approach that has been "tried, debated and analyzed for several decades" and has led to the persistent idea in education research that smaller classes can perk up student outcomes. Such thinking is certainly true in the United States. According to data from the National Center for Education Statistics, class size dwindled from 22.3 in 1970 to 15.3 by 2008; that represented 15 students for every one teacher. The Great Recession, however, pushed those numbers back up; by the 2011-2012 school year, the latest numbers available, the average elementary class size was 21.2 and the secondary class size was 26.8.

Yet, as the researchers' concluded, while "some evidence" suggests an impact on reading achievement after reducing class sizes, the effect is "very small." And the effect on math achievement "was not statistically significant."

So how could small class size impair learning? As explained in a Hechinger article, the thinking goes like this. The smaller the class sizes, the more teachers needed to cover the classes. It's possible that any new hires would "downgrade" overall teacher quality. And what would you rather have, asked author Jill Barshay? Placing your child "in a small class with an average teacher" or a "larger class with a good teacher"?

As the report concluded, maybe the funding dedicated to hiring more teachers could be better spent elsewhere.

The report is openly available on the Campbell Collaboration website.