Does class size influence student achievement?

IPP Policy brief n°28

Authors: Adrien Bouguen, Julien Grenet and Marc Gurgand

Contacts: julien.grenet@ens.fr, marc.gurgand@psemail.eu

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Summary

This 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.

Key Points

A certain number of international research studies, most of which are recent, estimate the effects of a reduction in class size on the progress of the pupils by convincingly neutralising selection bias.
Those studies show that halving the size of a class of 24 pupils by having two classes instead of one improves the mean performance levels of the pupils significantly, and it is even possible to see the long-term effects on academic pathways and occupational integration.
These effects are observed even when the teachers are not given specific assistance or support with their teaching.
The high cost of such a policy justifies targeting it on the most socially disadvantaged children, thereby working towards the goal of reducing inequalities.
Cost-benefit calculations indicate that such a policy is profitable whenever it enables the future salaries of its beneficiaries to increase by 1%, through its benefits on academic pathways.

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