I've seen the master keys for the ones at our school (Forgot a Combo once

) I'm pretty sure it was a 3-pin on the indiviual padlocks. For the lockers themselves, I think it's a 4 pin. Not that it really matters, considering anyone who's stupid enough to pick random lockers at a school will be disapointed and caught (security cameras, joy. </sarcasm>).
Otherwise, I'd spend time trying to learn how to pick the more complex 4, 5 and security pinned padlocks. They're much more fun and you don't make people think you're using these skills for a bad purpose. ( I Still can't get that Brinks!)