Well, officially school holidays start on the first of July. But generally most pupils don't give a damn towards late June, except those preparing for the Baccalauréat. I remember almost my entire class playing poker when I was 15 during some classes in the final weeks of school year, and I was in a really good school too! That's because most tests have already been sat for and that most resources from the French education system are redirected towards the massive burdenous organisation that is le Bac. Expect teachers being absent or classroom taken up for senior year final exams!
In short, most students are already on holiday, even if they're not supposed to be yet x) I hope to be proved wrong though!