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Brookings Institution report calls for larger class sizes, uses misleading data

New review finds "Class Size: What Research Says and What It Means for State Policy" report mischaracterizes prior research

EAST LANSING, Mich. (Jun. 16, 2011) –—A Brookings Institution report that suggests schools can save money by increasing class sizes without seriously affecting student achievement is based on a misleading summary of research on the benefits of class-size reduction, according to a new review released today.

The Brookings report, Class Size: What Research Says and What It Means for State Policy, was reviewed for the Think Twice think tank review project by Diane Whitmore Schanzenbach, associate professor in the School of Education and Social Policy at Northwestern University. The review was produced by the National Education Policy Center with funding from the Great Lakes Center for Education Research and Practice.

The report contends that the nation can save $12 billion annually by allowing class sizes to increase by one student, and that negative impacts from larger classes can be offset by better instruction that would result from laying off "least-effective" teachers.

In her review, Schanzenbach found that the Brookings report mischaracterizes prior research on the benefits of class-size reduction. The Brookings report consists mainly of a literature review of class-size research, and its "primary contribution is in summarizing what it deems to be high quality studies on the impact of class-size reduction," according to Schanzenbach.

While the report correctly states that only valid research should be used when assessing the benefits of class-size reduction, it "does not uniformly apply these standards to its literature review, and as a result the report presents misleading results," Schanzenbach said.

The Brookings report also claims that increasing class sizes is an effective cost-savings mechanism, asserting that allowing average class sizes to rise by one student will net a savings of $12 billion a year, or 2 percent of total spending on K-12 public education. Yet increasing the size of every class by one student isn't guaranteed to save money on teachers, even if schools get rid of the "least effective" ones, as is proposed in the report.

Schanzenbach offers the example of a hypothetical K-5 school with 24 classrooms: 100 students divided among 4 teachers in each grade. 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 said.

The Brookings report also ignores or mischaracterizes a growing body of research showing long-term benefits from smaller class sizes. A landmark study of 79 Tennessee elementary schools found that reducing the average class size from 22 students to 15 students vastly improved math and reading scores, especially among low-income and African American students. Even the Brookings Institution called the Tennessee study, known as Project STAR, "the most influential and credible study" of class-size reduction.

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 found that it fails to make the case that increasing class sizes can be cost-effective, while having no serious effect on achievement.

Find Diane Whitemore Schanzenbach's review and a link to the Brookings report at

The Think Twice think tank review project, 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 review is also available on the National Education Policy Center website at:


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