1) Inability to help students who are identified as fragile, or weak, or in need of help from their youngest years - thus perpetuating and even exacerbating social inequalities
2) Insufficient teacher training, both initially and as part of continuing education due in part to the preference for investing scarce resources into SELECTION instead of into training (I wrote about this, with as much humor as possible, in Sorbonne Confidential)
3) Failure to replace teachers who are absent in middle school and lycée, which leads to students losing ONE WHOLE YEAR of learning due to absent teachers who are not replaced as well as too few adults in the school.
4) Persistently poor results in foreign language learning, compared to other European countries
This is, of course, just a short list. And (since it is focused on failures) it does not mention the many successes.
The reason I mention it is to provide context for the current battle over what's called the "collège" (middle school) reform.
The first three points - all critical - are not dealt with at all. And the last point (languages) is deliberately made worse: the one thing that worked well will be destroyed.