In all honesty, biking in SF (high schools in particular) is super small. The bike scene a few years back (at Wash '06) was super dead (I'm not sure how it is now). I'm assuming it wouldn't be that huge. Like my previous posts before, I barely knew anyone riding there bikes at school. And you did say your school was a bad school. I'm guessing Balboa, Burton, or Mission, but biking isn't huge enough for anyone to jack your sh*t, yet. And plus most people like to drive to school or take MUNI.