Diane Whitmore Schanzenbach
William Mathis, NEPC
BOULDER, CO (June 16, 2011) – A Brookings Institution report that suggests schools can save money by increasing class size slightly without seriously harming student learning is based on an incomplete and misleading summary of research on the benefits of class-size reduction, according to a new review released today.
The report,Class Size: What Research Says and What It Means for State Policy, by Grover J. Whitehurst and Matthew M. Chingos, was reviewed for the Think Twice think tank research project by Northwestern University economist Diane Whitmore Schanzenbach.
The review is published by the National Education Policy Center, housed at the University of Colorado at Boulder School of Education.
The Brookings Report consists primarily of a literature review of class-size research followed by an argument that other policy options are more cost effective. The report asserts, for example, that $12 billion can be saved annually by allowing class sizes to increase by one student. It further claims that the negative impacts from larger classes can be offset by the improved instruction that would result from laying off the “least-effective” teachers.
Schanzenbach found that in its literature review the report correctly points out that only the most carefully constructed studies – those using experimental designs or those using sophisticated mathematical modeling – should be used when assessing the benefits of class-size reduction. She also found, however, that the report did not uniformly apply such standards in its literature review. According to Schanzenbach, the report places “too much emphasis on some mixed or negative studies that do not actually measure up to [their] expressed high standards.” As a consequence the report “presents misleading results.”
Schanzenbach notes in particular that the Brookings report gives insufficient weight to the single best study on class-size reduction, the Tennessee Student Teacher Achievement Ratio (STAR) experiment in which students and teachers in 79 Tennessee elementary schools were randomly assigned to small or regular-sized classes from 1985 to 1989. The new report downplays the power of the STAR experiment’s findings by mischaracterizing “the STAR effect sizes as unusually large relative to the literature.” Schanzenbach points out that the STAR is the only large, truly random experiment, so that study’s findings are “the most trustworthy estimates in the literature” and should accordingly be granted greater weight.
The Brookings report also completely fails to discuss the results of the evaluation of Wisconsin’s SAGE class size reduction program. This is a particularly curious omission since the SAGE results are discussed in, among other places, the 2002 Brookings publication, Bridging the Achievement Gap.
Further, while Schanzenbach credits the report for making “the important point that class-size reduction may be more effective for disadvantaged students and young students,” she also notes that the report ignores a growing body of research showing long-term benefits from class-size reduction that are not entirely reflected in short-term test scores.
Using its flawed literature review as a jumping off point, the report then asserts putative savings from allowing average class size across the U.S. to rise by one student, purportedly amounting to $12 billion a year, or 2 percent of total spending on K-12 public education. Schanzenbach points out the weakness of this logic by offering the example of a hypothetical K-5 school with 24 classrooms: 100 students in each grade, divided among 4 teachers. Reducing the teaching force by one would bring the average pupil-teacher ratio from 1:25 to 1:26. Yet it would be impossible to simply increase the resulting class sizes by a single student; instead, while most grades would have four teachers and a class size of 25, one grade would be cut to three teachers and class size would jump from 25 to 33.3. “Among the children in this grade, the negative impacts would be striking,” Schanzenbach explains.
In the end, Class Size: What Research Says and What It Means for State Policy fails to make the case that increasing class sizes is either relatively harmless or cost-effective. It is not a report that state policy makers can trust as a valid guide to policy making.
Find Diane Whitmore Schanzenbach’s review on the NEPC website at:
The Think Twice think tank review project (http://thinktankreview.org), a project of the National Education Policy Center, provides the public, policy makers, and the press with timely, academically sound, reviews of selected publications. The project is made possible in part by the support of the Great Lakes Center for Education Research and Practice.
The mission of the National Education Policy Center is to produce and disseminate high-quality, peer-reviewed research to inform education policy discussions. We are guided by the belief that the democratic governance of public education is strengthened when policies are based on sound evidence. For more information on NEPC, please visit http://nepc.colorado.edu/.
This review is also found on the GLC website at http://www.greatlakescenter.org/