IPP Policy brief n°28 - September 2017

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



logo-pdf-minDoes class size influence student achievement?




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.