You didn't ask me but I'll try to pass along some of the things I've learned from my wife about cooking classes.
Make sure everyone in your group is excited about it. More than anything it's a social occasion.
When picking which cooking school you want to go to look for one that focuses on teaching techniques important to the cuisine rather than those that just market themselves as about cooking and consuming a fabulous meal. For as much as you'll pay for the cooking class, you can get a better meal from a top restaurant. Therefore, learning something that you wouldn't necessarily understand from reading a book is important in how rewarding the class is.
A bonus is if the school includes a preliminary tour through a local market of the sort that professional chefs would shop at - that way you can learn some of the things they look for. For Paris, that's primarily the Bastille market but there are others.