As more parents try to enrol their children in private schools, new research from the Ministry of Education shows that there is a minimal difference between results in state and private sectors.
Most private schools are Catholic-run. They receive state subsidies, including teachers' salaries, follow the national curriculum and receive state inspections.
Fees are nominal and some two million of France's 12 million pupils are taught in the sector.
In the ministry's first comparative study of public and private systems, unadjusted statistics showed that pupils in private schools do better than those in the state sector. But when pupils' social and economic backgrounds were taken into account, the findings told a different story.
In fact, the study showed that the gap in achievement between the two sectors is minimal.
Private schools, which can select their pupils, taught a greater proportion of children from advantaged backgrounds characterised by more parental involvement and mothers with higher educational attainment. State schools were found to cater for a bigger share of socially disadvantaged children.
The picture is complex as many pupils move from one system to the other, and often back again, during their schooling. There is also a major shift from public to private at the start of the lower-secondary phase when parents hope that children in difficulty will benefit from a private school.
Yet the study noted that "departures from public to private and numerous changes (between the sectors) are always associated with slightly lower success".
The proportion of pupils in the two sectors has remained stable for the past 20 years, although more parents want to change to the private sector.
Some 12,000 extra pupils enrolled in private schools last September, but a further 50,000 could not find places.
While demand for private schooling is high, supply will remain low unless the government, which determines budgets and the number of teachers in schools, responds to calls from the governing body of Catholic education for greater state support and more teaching posts.
But there are no signs of a change in the politically sensitive financial balance between the public and private sectors.