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Peer Power: Students’ Classmates Have Greater Effect Than Other Factors on Academic Success

Study of San Diego Schools Suggests Reform Alternatives for Cash-Strapped Districts

SAN FRANCISCO, California, August 27, 2003 — What really affects the academic performance of elementary, middle, and high school students in California? A unique study released today by the Public Policy Institute of California (PPIC) examines achievement in more precise ways than has been possible in previous analyses – and it finds that students’ peers have a stronger effect on their achievement than the qualifications of their teachers or the size of their classes.

Using individual student-level data, rather than the grade-level data contained in the statewide data typically employed in such studies, the report draws into question whether some of the most highly valued school resources are really the primary determinants of student success. Conducted in collaboration with the San Diego Unified School District (SDUSD), the study analyzes gains in reading and math scores during the 1997-1998 through 1999-2000 school years, and finds that students made much greater gains in years when peers in their grade earned high scores on state standardized tests. The report finds, for example, that if an elementary student switches from a low performing grade-level peer group to a high performing one, the student’s gains in math scores will be 9 percent higher than they otherwise would have been.

Although the study found that teacher characteristics and class size can make a difference, they do not appear to affect student performance to the extent that many people believe. “Class size seems to matter more in lower grades, while teacher experience and level of education carry more weight in upper grades,” says PPIC senior fellow and UC San Diego professor of economics Julian Betts, who co-authored the study with PPIC research associate Andrew Zau and PPIC research fellow Lorien Rice. “These are clearly important factors, but our findings indicate that the achievement of a student’s peers is more influential. This leads to a powerful new idea: Programs to boost achievement of low-scoring students could ‘spill over’, benefiting all students at the school.” The report’s conclusions may provide new policy options for school districts that are trying to improve student achievement with limited financial resources.

Consistent with previous research, the study, Determinants of Student Achievement: New Evidence from San Diego, also found disturbing gaps between the academic achievement of poor and more affluent students: In SDUSD, a fifth grader attending a school at the highest socioeconomic level reads at the same level as a tenth grader attending a school at the lowest level.

The Public Policy Institute of California is a private, nonprofit organization dedicated to improving public policy in California through independent, objective, nonpartisan research on major economic, social, and political issues. The institute was established in 1994 with an endowment from William R. Hewlett.

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