Key Lessons: Class Size and Student Achievement

After more than 20 years of research, class size continues to be at the forefront of the educational and political agenda for schools, school districts, and school boards. Here is a snapshot of what research tells us about class size and student achievement.

After more than 20 years of research, class size continues to be at the forefront of the educational and political agenda for schools, school districts, and school boards. Since the late 1970s, research has indicated that reduced class sizes (15 to 18 students) are associated with increased student achievement in specific situations, particularly when small classes are implemented in the primary grades and students participate in small classes for more than one year. Following is a snapshot of the significant findings from the research:

  • Smaller classes in grades K-3 improve student achievement in reading and math.

    Students in smaller classes performed better than students in larger classes on reading and mathematics achievement tests (Mitchell & Mitchell, 1999; Molnar, Smith, & Zahorik, 1999).

  • A class size of 15-18 is the upper limit for capturing benefits in the early grades.

    Classes with no more than 15-18 students have been found to be the threshold class size for increasing student achievement in the early grades. (Ehrenberg, Brewer, Gamoran, & Willms, 2001).

  • Young students benefit more when reduced class size programs span grades K-3.

    The achievement of students in small classes outpaces that of students in larger classes by a widening margin for each additional year spent in small classes. (Fidler, 2001; Nye, Hedges, & Konstantopoulos, 2001a).

  • The benefits of small classes in the primary grades are lasting.

    The reading and/or math gains students in small classes experience in the primary grades continue or are maintained more than five years later (Nye, Hedges, & Konstantopoulos, 2004; Nye, Hedges, & Konstantopoulos, 2001b).

  • Small classes in the primary grades can help close the achievement gap.

    Minority students often experience even greater gains than white students when placed in small classes in the primary school years. Minority students tend to have lower achievement scores than white students before participation in small classes and make larger achievement gains by the end of the year. (Nye, Hedges, & Konstantopoulos, 2004; Nye, 2000; Molnar, Smith, & Zahorik, 1999).

  • More instructional options for teachers might explain the benefits of small classes.

    Teachers may teach differently or certain instructional strategies may work better in small classes. For example, more work done in small groups might be possible. (Ehrenberg, Brewer, Gamoran, & Willms, 2001).

  • Teachers with small classes give more individual attention to students.

    High school math teachers with small classes were found to engage with individual students and small groups more frequently than teachers with larger classes, possibly because they spend less time on classroom management than teachers in larger classes (Rice, 1999).


Click the "References" link above to hide these references.

Ehrenberg, R. G., Brewer, D. J., Gamoran, A., & Willms, J. D. (2001). Class size and student achievement. Psychological Science, 2, 1-29.

Fidler, P. (2001). The impact of class size reduction on student achievement. Los Angeles, CA: Los Angeles Unified School District, Program Evaluation and Research Branch.

Mitchell, D. E., & Mitchell, R. E. (1999). The impact of California's Class Size Reduction initiative on student achievement: Detailed findings from eight school districts. Riverside, CA: University of California, California Educational Research Cooperative.

Molnar, A., Smith, P., & Zahorik, J. (1999). Evaluation results of the Student Achievement Guarantee in Education (SAGE) Program, 1998-99. Madison, WI: University of Wisconsin Madison, School of Education.

Nye, B., Hedges, L. V., & Konstantopoulos, S. (2004). Do minorities experience larger lasting benefits from small classes? Journal of Educational Research, 98, 94-100.

Nye, B., Hedges, L. V., & Konstantopoulos, S. (2001a). Are effects of small classes cumulative? Evidence from a Tennessee experiment. Journal of Educational Research, 94, 336-345.

Nye, B., Hedges, L. V., & Konstantopoulos, S. (2001b). The long-term effects of small classes in early grades: Lasting benefits in mathematics achievement at grade 9. Journal of Experimental Education, 69, 245-257.

Nye, B. A. (2000). Do the disadvantaged benefit more from small classes? Evidence from the Tennessee class size experiment. American Journal of Education, 109, 1-25.

Rice, J. K. (1999). The impact of class size on instructional strategies and the use of time in high school mathematics and sciences courses. Educational Evaluation and Policy Analysis, 21, 215-229.

Reprinted from the Center for Public Education, Associates for the Center for Public Education. (2005). Key Lessons: Class Size and Student Achievement. Washington, DC: Center for Public Education.


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