Media Briefings


  • Published Date: March 2009

Smaller class sizes and fully trained teachers make a significant difference to children’s educational outcomes, according to new research by Pascal Bressoux, Francis Kramarz and Corinne Prost, which looks at data on the French school system.

The study, which is published in the March 2009 issue of the Economic Journal, takes advantage of an administrative mistake in forecasting the number of teachers needed in France in 1991, as a result of which some novice teachers started their jobs before receiving any training. Analysis of this event finds that:

  • The final test scores in mathematics for students with a trained teacher are substantially larger than the scores they would have had if their teachers had not been trained.
  • This effect is not related to teachers’ ages since trained and untrained teachers were on average the same age. But it could reveal an experience effect through the on-the-job experience included in the training programme.
  • Smaller class sizes also improve student achievement. Training teachers is equivalent to reducing class size by 10 students in terms of final test scores in mathematics.
  • The effect of class size is more beneficial for low-achieving students within classes. But low-achieving students do not seem to benefit from the training of their teachers. This suggests the importance of examining how resources affect different students differently.

There is a debate between those who think that it is more efficient to improve the quality of teachers and those who believe that decreasing the size of the classes has a more direct impact on students’ achievements.

One way of improving teacher quality is through training. Yet it is very difficult to evaluate the effect of training since trained teachers are usually not assigned to the same classes as untrained teachers and disentangling the impact of the kind of classes and the one of training needs a lot of data on the characteristics of the students and the classes.

This study analyses an accidental French experiment, when thanks to administrative mistakes in forecasting the number of teachers, trained and untrained novice teachers were similar. This makes it possible to assess the effect of training via a comparison of untrained novice teachers and trained novice teachers. The effect of class size can be evaluated with the same data.

In France, recruitment of teachers in state schools is based on competitive examinations. When students pass the examination, they become civil servants in traineeship and are trained in specific colleges. After their traineeship, young teachers get tenure.

The number of slots in the training colleges is limited and determined each year by the regional administration, using forecasts for teachers’ positions. All applicants are ranked according to their grades in this examination. The students ranked first start their training. Students who are ranked just after the last admitted candidate on this primary list are assigned and ranked within a waiting list.

In September, the number of vacant job slots is often greater than the one expected two years earlier. Students who have finished their training are assigned to some of these job slots, and, in October, some students on the waiting list are assigned to the vacant slots. Hence, these students have to teach a class for an entire school year without receiving any training. They start their training the year after.

The design of this study relies on a specific year, 1991, which ends a series of forecasting errors leading to a large increase in the number of untrained teachers. So the untrained novice teachers, who had taken the entrance examination in 1991, had very good rankings and would have been selected for entry had they competed for the examination during another year, and especially during the year 1989, when the trained novice teachers passed their entrance competitive exam.


Notes for editors: ‘Teachers’ Training, Class Size and Students’ Outcomes: Learning from Administrative Forecasting Mistakes’ by Pascal Bressoux, Francis Kramarz and Corinne Prost is published in the March issue of the Economic Journal.

Bressoux is at the University of Grenoble 1. Kramarz and Prost are at the National Institute of Statistics and Economic Studies (INSEE) and the Center for Research in Economics and Statistics (CREST) in Paris.

For further information: contact Corinne Prost on +33 1 41 17 54 42 (email:; or Romesh Vaitilingam on 07768 661095 (email: