Does class size influence student achievement?

International audienceThis policy brief presents the results of the most methodologically robust studies that estimate the impact of a reduction in class size on the student achievement and longer-run outcomes. Contrary to an idea that persisted for a long time, the effects are high, if they are compared with those of other educational policies conducted on a large scale and assessed rigorously. The absolute cost of such a policy justifies targeting it on the most disadvantaged pupils, but the investment is profitable whenever the salary gain for two years spent in a half-size class is greater than 1%. However many unknown quantities remain, in particular about how reduction in class size links up with teaching practices