Howdy there! I teach English and sponsor a gaming club at a middle school (grades 6-8) in Sugar Land, TX. We meet once a week, and it's great fun! In the beginning, I had to DM everything, but after a couple of years I have some excellent student DMs. We mostly run published adventures from Dungeon or the Dungeon Crawl Classic series. Some thoughts on setting up a new club:
1. Check it out with your administrators first. Ultimately, they decide what does and doesn't happen on their campus. Make no assumptions about tolerances for the game.
2. At the first meeting, I sent them home with a note to their parents... sort of a persmission slip. I wanted the parents to know what their kids were up to, and to dispel a few common misunderstandings about the game. As a parent myself, I'd want to know what my kids were up to. I'd definitely approve of MY kids playing D&D, but some parents might not. Again, make no assumptions. You'll save yourself some issues later on if all the moms and dads know what's going on.
3. Also at the first meeting, explain to the kids what it's all about, and maybe walk them through a silly, quick encounter (I used "The Orc and the Pie" for this).
4. For teaching the game to new, young players, the box sets are awesome. It's a very basic adventure from an experienced players point of view, but it's great for teaching the game.
5. As soon as you're set up and running, get some student officers to help you run the club. It will make it easier and more enjoyable for you and them.
I have a ton of handouts, letters to parents, officer responsibilities, etc. If you'll reply (and we can figure out how to exchange emails without the whole world seeing them), I'll be happy to share everything I have, and pass along anything else I can think of!
Good luck!