I can’t say it will be the same for you, but here is what we did to sign up for French public middle school in Paris. By the way, middle school is called “Collège” in France. (See below for caveats).
The first step is to call CASNAV. Call CASNAV and book an appointment for a placement test. The main phone number is 06 11 96 39 06. You can also book an appointment online.
What is CASNAV? CASNAV is the central organization for enrolling/registering students new to the French school system who are in middle school or high school. Elementary school children are allocated/registered at the Marie (city hall) but not older kids. I think that is because they expect that it is easy enough to integrate non-french speakers when they are elementary school level but that they need special programs as they get older.
How long does it take to get an appointment? There was a really long lead time for booking a spot for testing. The lead time about a month in Jan 2018. I looked recently and it was still about a month.
Where does the testing take place? The testing is done at the CASNAV office in the 19th.
What is the test like? It is a simple written and oral test. My impression is that unless your child is really good at french they will be put into the NF (non-francophone) program. You will be assigned to the closest NF program to your residence. By the way, the official name for the program is Upe2a ,
What school will you be assigned to? Not all schools have the “NF” program. Later in the year most programs are full so you may be allocated really far from your home (like we were). My understanding is that if you start in Sept you will be more likely to get the school closest to your home. The website has a page which shows schools which have an NF program. There does seem to be some leeway as to which school you are assigned to so it makes sense to do some research beforehand.
What is the NF program like? There are students from all over In Fille’s class there were students from China, Brazil, Taiwan, Japan, Thailand and Africa. Most but not all of their time is spent learning french. The french teacher groups them by level. If a student starts mid-way through the year they are on their own path but she tries to integrate them. Other subjects are also taught in french (e.g. math, music, geography) but specifically for the NF students so at a slower pace with attention to their level of French.
How long is the NF program? Your child stays in the NF program as long as your child needs to. Along the way they will be partially integrated into the regular french program – that is, for certain subjects. Fille was integrated in the regular program for math and english after 3 weeks in NF. Another family I know was partially integrated after 3 months into math and history. It all depends on what the NF teacher thinks will be good for them. There was a boy in Fille’s class who had Japanese as his native language. After a year he is still not integrated for any subjects!
Caveats. I do not know how to sign up ahead of time for school if you are currently abroad. I do not know how to sign up for school if you are fluent in French. I’m also not 100% positive about the process for kids in elementary school. Sorry! I’ll try to find out and let you know. Or you can always call Casnav!