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).

Resources On Class Size And Student  Achievement

The following organizations offer information on class size and student achievement. (Note that if you select an organization's web site link, you will leave the Center for Public Education web site.)

The SERVE Center for Continuous Improvement
University of North Carolina at Greensboro
915 Northridge St.
Second Floor
Greensboro, NC 27403
Phone: (800)755-3277

The SERVE Center supports the continuous improvement of education for all learners in the Southeastern United States and operates the Regional Educational Laboratory for the Southeast, providing research-based information and services around the United States. Resources and publications on class size reduction programs include How Class Size Makes a Difference, A Parent's Guide to Class Size Reduction, Longitudinal Findings from a District's Reduced Class-Size Initiative, and Observing Life in Small Class-Size Classrooms.

Health and Education Research Operative Services
PO Box 1271
Lebanon, TN 37088
Phone: 615-449-7904

HEROS is a nonprofit organization that evaluates and assesses programs for children, families, and communities. HEROS conducted the original four-year evaluation of Tennessee’s Project Student/Teacher Achievement Ratio (Project STAR). The data collected through this evaluation was made public and many researchers have conducted additional analyses, usually to determine if the smaller class sizes were more effective for subgroups of students (e.g., minority students, low income students.)

Student Achievement Guarantee in Education Program (SAGE)
Wisconsin Department of Public Instruction
125 S. Webster Street
Madison, WI 53707
Phone: 800-441-4563

The Student Achievement Guarantee in Education Program (SAGE) has four components: reduced class sizes (no more than 15 students to 1 teacher in grades K-3), collaboration between schools and communities, implementation of a rigorous curriculum, and a new professional development and staff evaluation program. An ongoing evaluation of the program has been conducted since its inception and continues to show increased student achievement for students in classrooms with smaller class sizes.

Class Size Matters
124 Waverly Place
New York, NY 10011
Phone: 212-674-7320

Class Size Matters is a grass roots organization of parents and others concerned with the large classes sizes in New York State, and specifically, New York City. In advocating for and promoting smaller class sizes, the organization disseminates information related to the benefits of smaller class sizes and lobbies for policy changes to ensure small class sizes are available for students.


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.

This document was prepared by Caliber Associates for the Center for Public Education. Caliber, an ICF company based in Fairfax, Va., specializes in social science research and evaluation.

Posted: July 25, 2005