I have no experience with any particular language schools, but if you want to learn french in paris for free there is a language library at the pompidou center on beaubourg and you can spend as much time as you want there, everyday except tuesday, when they are closed. They are open from about 11 or noon until 930 every night.
All you do go to the desk on the first floor, tell them what your mother tongue is, what language you want to learn and your preferred mode of learning, via listening to a cassette or watching a dvd.
each time they hand you a piece of paper, alloting one hour, but if it isn't busy, you can just go again and again, all day long. i was there yesterday, and there was a french guy learning italian on one side of me, a tibetan guy learning english on the other, and an american ex-pat learning thai next to him.. it's pretty cool
hope this helps, i came to france knowing very little french, and after a couple months i am able to converse nearly fluently..cheers