Does reducing class size significantly improve student achievement?

Does smaller class size actually boost test scores?

The short answer is: not much, and not for everyone. A 2025 analysis of Korean students found that for 6th graders, being in a class of 20 or fewer students showed no clear overall effect on academic achievement compared to larger classes [4]. For 9th graders, the average effect was also not statistically significant, though some models showed small gains for classes with 22 or fewer students [4]. This means that simply shrinking class size does not guarantee higher test scores.

A 2025 study of high school students found that larger classes only reduced test scores in classrooms with high levels of disruption—where students were misbehaving or off-task [5]. In calm, well-managed classrooms, class size had no measurable effect on test scores. Even in disruptive settings, the negative impact of a larger class was small, suggesting that class size is not a primary driver of student success [5].

A 2024 study of accounting students actually found that larger class sizes had a positive effect on academic performance, possibly because students had more opportunities for collaboration and peer tutoring [3]. This counterintuitive finding highlights that the relationship between class size and achievement is not simple or one-directional.

When does class size matter most?

Class size matters more for certain groups and in certain contexts. For students with special educational needs, smaller classes are strongly preferred by teachers and students because they allow for more individualized instruction and teacher attention [1]. However, a 2023 systematic review found virtually no high-quality quantitative studies on this topic, so the evidence is based on qualitative reports rather than hard data on test scores [1].

A 2025 study found that the effect of small classes varies by region. In Korean medium-sized cities, small classes (22 or fewer students) showed positive effects on 6th and 9th grade achievement, but in large cities the effect was negative for 6th graders [4]. In rural areas, the effect was weakly positive for 9th graders [4]. This suggests that the benefits of smaller classes depend on the local educational environment, not just the number of students.

A 2024 analysis of data from 21,903 schools across 80 countries found that the relationship between class size and achievement is not linear. The study identified a critical threshold of 27 students per class: below that number, the relationship was predictable; above it, outcomes became unpredictable and nonlinear [2]. This means that reducing a class from 30 to 28 might have a different effect than reducing it from 25 to 23.

What about student engagement and satisfaction?

Even if test scores don't change much, smaller classes can improve how students feel about their learning. A 2022 study of business students found that students in larger classes perceived lower levels of teacher interaction and satisfaction [6]. However, the same study found that student involvement and teacher interaction were the key drivers of learning outcomes and satisfaction, regardless of class size [6]. So while smaller classes may make it easier for students to engage, it's the quality of teaching and student effort that ultimately matters.

The 2023 review of special education found that students and staff consistently preferred smaller classes because they allowed for more individualized instruction and teacher attention [1]. This suggests that even if test scores don't rise, smaller classes may improve the educational experience for students who need extra support.

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