Class Size Matters

In one of the National Education Policy Center’s most often-cited policy briefs, Does Class Size Matter?, Diane Whitmore Schanzenbach, a professor at Northwestern University, reviews the research comprehensively and reaches a clear set of conclusions. The five facts below are based on the analysis she presents in her brief.

1. Smaller classes in early grades are associated with better test scores: The largest and most rigorous class size study ever conducted (Tennessee’s Student Teacher Achievement Ratio, or STAR, experiment) found, in no uncertain terms, that students in smaller classes of 13 to 17 students in grades K-3 outperformed their peers in larger classes of 22 to 25 students: STAR found that all students benefited, on average, from the 13- to 17-student classes. However, African American students and students from low-income families benefited even more. Most quasi-experimental studies reach similar conclusions. It’s worth noting that the vast majority of high-quality class size research focuses—as the STAR study did—on the early grades, so more research is needed in this area. An exception is a study that found that smaller eighth-grade class sizes are associated with higher rates of student achievement and engagement, especially in urban schools.
2. Smaller classes in early grades are associated with better long-term outcomes: These outcomes include lower rates of juvenile crime, higher rates of high school and college completion, and increased odds of saving money, marrying, and owning a home. 
3. Class size reduction helps, even if classes remain large: Some researchers have concluded that class size reduction only helps if class size drops below a magic number like 15. However, the preponderance of evidence suggests that reductions can improve student achievement even when class size remains as high as 40.
4. Class size reductions make an even bigger difference for experienced teachers: Although all teachers benefit, on average, from class size reductions, experienced teachers are better able to take advantage of the smaller class sizes. With smaller classes, teachers can spend more time on instruction and less time on classroom management. They can more closely monitor student learning. They have more time to use alternative approaches to re-teach concepts to students who do not get them the first time. And they have higher-quality personal interactions with their students.