My parents moved us to rural France when I was 11 ( in 2001), straight into french state school. There was little extra support for us and although we were all fluent within about a year, it was only as an adult (living in Paris ) that I really learnt and understood all of the little grammar rules.
Our days were so long, and I went from year 6 in the UK to the second year of collège in France. School started at 7.50 and didn't end until 17.30 and then 18.30 when we were in Lycée.
A lot of pressure with constant tests that are marked, effort was not taken into account!
My sister and I disagree on a lot of things, but one thing we do agree on is that we will never put our children in french school! And yet, it's not because we aren't academic, my sister has a doctorate and works as a researcher for a swiss uni, and I stopped at masters.
If you are going to put your children in French school, you will need to support them and advocate for them. And help them with their homework.
Here is a screenshot of the 2017-18 school hols for Cherbourg. As your son is 14 he would be going into "seconde" I imagine which is the first year of lycée.
Here is a quick breakdown of the lesson hours for that year per week :
Core obligatory subjects
French 4 hours
History Geography 3 hours
Foreign Language (at least 2) 5.5 hours
Maths 4 hours
Biology 1.5 hours
Physics and chemistry 3 hours
Civic Legal and Social 0.5 hours
Sport 2 hours
Individual support (Never had this but it's in guidelines) 2 hours
Total 25.5 hours
Complementary subjects Each student must have at least 2
Principes fondamentaux de l'économie et de la gestion 1 h 30
Création et innovation technologiques 1 h 30
Santé et social 1 h 30
Biotechnologies 1 h 30
Sciences et laboratoires 1 h 30
Littérature et société 1 h 30
Sciences de l'ingénieur 1 h 30
Méthodes et pratiques scientifiques 1 h 30
Langues et cultures de l'Antiquité (latin ou grec) 3 h
Langue vivante 3 3 h
So it's at least 28 hours of lessons a week plus about 10-15 hours of homework!