Article dans une revue: French children start public school either the year they turn two or the year they turn three. We evaluate the impact of this unique schooling policy on maternal labour supply. Using a Regression-Discontinuity design, we show that early school availability has a significant employment effect on lone mothers, but no effect on two-parent families. Also we show that the effect grows larger as the child grows older and as the family loses eligibility for child benefits. Finally, we provide some new evidence that school enrolment at the age of two has no adverse effect on children's subsequent educational outcomes.