The Washington State Institute for Public Policy analyzed whether reducing class size in the K–12 school system leads to better student outcomes and whether benefits exceed
costs. To investigate, we conducted a systematic review of research by collecting all studies we could find on the topic. We screened for scientific rigor and, for our analysis, only included
those studies with the strongest research methods. Most studies were from the United States, while some were from other industrialized countries. We identified 53 credible evaluations of whether class size reductions have a cause and effect relationship with student outcomes.
Most of the 53 studies in our review measured student outcomes with standardized test scores; a few examined high school graduation rates. Policymakers, understandably, want schools to produce other outcomes as well, but test scores and school completion are most often measured in the existing research literature.
Our bottom line finding: In the earliest K–12 grades, reducing class size has a high probability of producing a favorable outcome — that is, where the long – term benefits of reducing class size consistently exceed the costs. In the upper grades, on the other hand, reducing class size poses a substantial risk of an unfavorable outcome — that is, where costs may often exceed benefits.
Next steps. In an upcoming Institute report, due October 2013, the magnitude of this effect will be compared with other educational policy options under consideration in Washington State. We
will apply the Institute’s economic model to estimate the relative benefits and costs of a variety of evidence – based policy options that improve educational outcomes.
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