Class Size and Student Achievement

The Reference Desk has received a number of questions recently about the impact of factors like class size, school size, and grade configuration on student achievement. This week’s entry focuses specifically on class size and features resources that summarize key studies and other relevant research on this topic. In the coming weeks, we will look at how other aspects of school structure may affect student achievement.

Question

What does the research say about the effect of class size on student achievement?

Research Synopsis

Reference Desk researchers found several resources related to the impact of class size on student achievement. Evidence suggests that when “planned thoughtfully and funded adequately,” students in smaller class sizes in kindergarten through third grade show gains in reading, language arts, and mathematics (Biddle and Berliner, 2002; see below). Other studies demonstrate that students in smaller classes outperform students in regular-size classes on achievement tests (Reichardt, 2001; see below). In addition, some resources point to the impact of small class size on different student subgroups. One report suggests that, “Small classes help minority and low-income students the most. Teachers in smaller classes give students more individual attention and have fewer discipline problems” ( Thompson, 2001; see below).

Publicly Available Resources

Reducing Class Size: Choices and Consequences. Reichardt, R.; Aurora, CO: Mid-Continent Research for Education and Learning; April 2001; 8 pages.

“The strongest evidence that smaller class sizes improve student performance comes from Tennessee [STAR Study, which]… found that students in the small classes significantly outperformed students in regular classes on standardized reading and mathematics tests…. Subsequent studies found that students from the smaller classes continued to outperform students from the regular-size classes on achievement tests through middle school, with some indication of improved performance and behavior through high school…. Test scores of minority students improved more than those of non-minority students.”
What Research Says about Small Classes and Their Effects. Biddle, B. J., and Berliner, D. C.; San Francisco, CA: WestEd; 2002; 24 pages.

“Findings so far available have indicated larger gains for students from small classes—in achievement scores for language arts, reading, and mathematics—that are roughly comparable to those from the STAR project” (p. 12). One of the major conclusions put forth by the authors is that “[e]xtra gains from small classes in the early grades are larger when class size is reduced to less than 20 students.”
First in America Special Report: The Lessons of Class Size Reduction. Thompson, C. L., and Cunningham, E. K.; Chapel Hill, NC: North Carolina Education Research Council; October 2001; 5 pages.

“The evidence that smaller classes promote increased learning is strongest in grades K–3. The longer students are in small classes, the more they benefit. Small classes help minority and low-income students the most. Teachers in smaller classes give students more individual attention and have fewer discipline problems. Though research in California and Wisconsin has found positive results of small class size, the states faced several barriers to reducing class size, including a shortage of high-quality teachers; lack of adequate facilities, equipment, and materials; and lack of sufficient funding.”

The Reference Desk also found these organizations and resources to be helpful in learning more about the effect of class size on student achievement:

SERVE Center
This organization’s website provides a list of articles and resources about class size reduction.
Key Lessons: Class Size and Student Achievement.

This resource from the Center for Public Education lists key lessons learned about class size and achievement, with primary references. The “focus is on K–3, the ages for which most research on class size has been conducted. Overall, the research suggests that smaller class sizes (18 or fewer students) is linked to achievement and has lasting effects, especially when class size is reduced over multiple years.

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