pwalther: Here's a site that tells about how to run raffles in California
caag.state.ca.us/charities/faq.htm#raffle1
Now, whether there's any legal distinction in a simple prize drawing at a school event and a "raffle" is a question I can't answer.
We stay away from the true raffles where you are pre-selling tickets, leaving the person with a stub, drawing the prize later, etc. Not that there's anything wrong with that, it's just what we do are the simple, place-a-ticket-the-jar type thing where everything happens that night in front of the whole group.
As I say, legally I don't know if there's a difference. As a matter of practicality, those who govern this really don't seem to want to know about the simple little drawings we are having.
Naturally - the first time there's ever a problem or a question of fairness, that would all change!
Good luck!