aftr sleeping on it, I came up with a few more:
American History X
Billy Madison
The Craft
Bye Bye Birdie
D3: The Mighty Ducks (the one set in the prep school)
Mean Girls (I'll be honest: I haven't watched the whole thing, but it has Lacey Chabert. That's good enough for me.)
Den Osynlige (or if you prefer english-speakers, it was remade sometime later as
The Invisible)
Friday Night Lights
Rebel Without a Cause
one I thought could warrant mention, but was not sure if it could be typified as "high school-themed" would be
Murder by Numbers. Also, I have no idea where
Cruel Intentions fits in; I thought it was a college-based setting, but I cannot recall exactly.
and Woods, you were right about
Stand by Me; it doesn't fit. I must've been thinking of another title with four friends, but it came out wrong.
Stand by Me takes part almost solely in the wild outside, so yeah, my mind was most certainly wandering. For some reason, I can't think of the name of it anymore.
one last comment:
Back to the Future should definitely count. I'd say most of the film either revolves around the high school, the JC Penny's parking lot, the Prom/Homecoming Dance, and Doc Brown's place. It's a great high school flick.