A French experiment of the early 2000s reduced first-grade (cours préparatoire) class size to about 10 pupils in 100 classes, contrasted with 100 full-size classes of about 21 pupils; following pupils to the end of Grade 2, Bressoux, Lima and Monseur (2019) found significant contemporaneous achievement gains in Grade 1 but no carryover into Grade 2. Whether such gains persist beyond Grade 2 — into later schooling and adult outcomes — and whether persistence depends on the size of subsequent classes and on teacher experience remains unknown for France: no long-run follow-up of any French class-size-reduction cohort has been published, the ministry's evaluation of the 2017+ dédoublement policy (halving CP/CE1 classes in priority-education schools to about 12 pupils) extends only to the end of Grade 2 and finds limited or null effects, and the existing cost-effectiveness analysis (2025) projects long-run returns from short-run achievement effects rather than measuring them. The problem is to measure the full fadeout profile of Grade-1 class-size reduction in France, to test its moderators (subsequent class size and teacher experience), and to ground the policy's cost-effectiveness in measured long-run outcomes.

Background

Whether reducing the number of pupils per class improves achievement, and whether any improvement lasts, is a long-standing question in the economics and psychology of education. The reference point is Project STAR (Student/Teacher Achievement Ratio), a 1985–1989 randomized experiment in Tennessee that assigned pupils in kindergarten to grade 3 to small (13–17 pupils) or regular (22–25 pupils) classes and found short-run gains, with evidence of long-run benefits in adulthood (Krueger, 1999; Dynarski, Hyman & Schanzenbach, 2013; Chetty, Friedman, Hilger, Saez, Schanzenbach & Yagan, 2011). Quasi-experimental studies in other countries give smaller or null effects (Angrist & Lavy, 1999; Fredriksson, Öckert & Oosterbeek, 2013), and a 2025 meta-analysis correcting for publication bias concludes that the implied class-size effect on achievement is close to zero for every identification approach except Project STAR (Opatrny, Havranek, Irsova & Scasny, 2025). A recurring pattern in this literature is that contemporaneous effects (gains while the small class is in place) are larger and more robust than carryover effects (gains that persist after pupils return to normal-size classes); the robustness of STAR's carryover effects has itself been questioned (Sohn, 2015), and a second year in small classes appears to add little (Konstantopoulos & Li, 2012).

France provides an unusually clean instance of this question. In the early 2000s a French experiment reduced first-grade class size — cours préparatoire (CP), the first year of French elementary school, at age about six — in 100 classes (average 10.5 pupils, range 8–12), contrasted with 100 full-size classes (average 21.3, range 15–27); pupils were followed for two years to the end of Grade 2. Bressoux, Lima and Monseur (2019) analysed this experiment with multilevel growth curve modelling (hierarchical regression models in which each pupil's achievement trajectory over time is nested within their class) and found a significant positive contemporaneous effect of the reduction in Grade 1 but no carryover the following year: by the end of Grade 2 the effects had faded. A separate large-scale French investigation of first-grade literacy also found modest class-size effects (Ecalle, Magnan & Gibert, 2006). From 2017 France generalized the idea in priority education — REP and REP+ (réseaux d'éducation prioritaire) are networks of schools in disadvantaged areas receiving extra resources: CP and then CE1 (Grade 2) classes there were halved to about 12 pupils (the dédoublement policy). The ministry's evaluation directorate, the DEPP, evaluated this policy through the end of CE1 (Andreu et al., 2021), finding limited or null effects on pupil progress, concentrated in mathematics among the weakest pupils, and collected teacher-practice data in a companion multidimensional evaluation (Vourc'h, Charpentier & Lima, 2021). A 2025 analysis by the Conseil d'analyse économique projects that the primary-level dédoublement pays for itself in the long run, but its long-run returns are extrapolated from short-run achievement effects through an assumed class size → achievement → future earnings chain, not measured on French cohorts (Fajeau, Grenet, Laveissière & Leonetti, 2025).

The unresolved scientific question is the temporal profile and the conditions of persistence of Grade-1 class-size benefits in France. The source experiment observed pupils only one year after treatment ended, had no data on the size of the Grade-2 classes pupils subsequently attended, was not strictly randomized, did not observe the instructional mechanisms behind the teacher-experience moderator its models estimated, and produced no cost-effectiveness comparison.

Problem Statement

The problem is to establish, for French first-grade class-size reduction, whether the contemporaneous achievement gains persist and under what conditions — the complete evaluation of the temporal profile of the class-size benefit that determines the policy's long-run value for money. Specifically:

  1. Long-run persistence (fadeout profile). Using longitudinal data on cohorts exposed to Grade-1 class-size reduction — the early-2000s experimental cohort and/or the post-2017 dédoublement cohorts in REP/REP+ — estimate whether achievement effects persist beyond Grade 2 into later primary and secondary schooling and, where data linkage permits, into educational attainment and adult outcomes, or fade entirely, quantifying the effect at each follow-up horizon.

  2. Moderators of persistence. Test whether persistence or fadeout depends on the size of the classes pupils attend after the reduced year (the Grade-2 class-size moderator that the source experiment could not examine) and on teacher characteristics — in particular Grade-1 teacher experience.

  3. Causal identification. Establish these estimates causally despite the non-random assignment of the original experiment, reporting the identifying assumptions and robustness checks on which the claims rest.

  4. Measured cost-effectiveness. Combine the estimated persistence profile with cost data to assess the cost-effectiveness of Grade-1 class-size reduction relative to alternative uses of the same resources (e.g., teacher tutoring or 'more teachers than classes' schemes), grounding the benefit side in measured long-run outcomes rather than purely projected ones.

These four parts jointly serve one overarching objective — the complete temporal and conditional evaluation of the Grade-1 class-size benefit in French early schooling. The objective is a measured answer to the persistence question from the best available French cohort data, with the moderator tests and the cost-effectiveness assessment grounded in that measured result rather than in an identification strategy alone.

References

  1. Bressoux, P., Lima, L., & Monseur, C. (2019). Reducing the number of pupils in French first-grade classes: Is there evidence of contemporaneous and carryover effects? International Journal of Educational Research, 96, 136–145. DOI: 10.1016/j.ijer.2018.10.006. https://doi.org/10.1016/j.ijer.2018.10.006
  2. Andreu, S., Ben Ali, L., Blouet, L., Bressoux, P., Charpentier, A., Cioldi, I., Lacroix, A., Lima, L., Murat, F., Odin-Steiner, D., Raffaëlli, C., Rocher, T., & Vourc'h, R. (2021). Évaluation de l'impact de la taille des classes de CP et de CE1 en REP+ sur les résultats des élèves et les pratiques des enseignants (DEPP, Série Études, Document de travail n° 2021.E04). HAL: hal-04782796. https://hal.science/hal-04782796
  3. Vourc'h, R., Charpentier, A., & Lima, L. (2021). Dédoublement des classes de CP et CE1 en REP+. Résultats de l'évaluation multidimensionnelle : impacts sur les élèves et évolution des pratiques (presentation at 'Les jeudis de la DEPP', Paris, October 2021). HAL: hal-04782911. https://hal.science/hal-04782911
  4. Merle, P. (2022). Le dédoublement des classes de CP et CE1 : quel bilan ? La Vie des idées, 31 May 2022. HAL: hal-04113462. https://hal.science/hal-04113462 ; https://laviedesidees.fr/Le-dedoublement-des-classes-de-CP-et-CE1-quel-bilan
  5. Fajeau, M., Grenet, J., Laveissière, E., & Leonetti, O. (2025). Efficacité économique de la réduction de la taille des classes (Conseil d'analyse économique, Focus n° 113, May 2025). HAL: halshs-05458927. https://shs.hal.science/halshs-05458927
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