Our school allows nothing electronic, PSP's, iPods, cell phones, etc...
No video game tournaments or anything of the like either. Buuut, they never actually said anything about DS's. I used to bring it in when I was obssessed with beating MPH.
As for flash game, they're not allowed either, but people play them anyways. The key is to go into any computer lab but the library, since pretty much every site you go on gets blocked the next day. If it's any other room, you can access an un-blocked site any time. Speaking of blocked sites, they even block the google search for "Proxy". xD