I think my pick would be the Breakfast Club. I live in Illinois now (like Hughe's did for much of his life, basing many of his films or their settings off of the Chicago area), but at the time I really had never heard of a "breakfast club" or weekend detention. But now that both my kids have attended high school here, I see this is a common thing. At their school they call it "Saturday School." I still think it's strange.
I have to say though, that I really liked Ferris Bueller's Day Off a lot too. It was just a fun movie but with a lot of good lessons.