A lot of them weren't really that well-known at the time. If this same cast would have been in the movie at the peak of their careers, the movie would have proved far too expensive to make.
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"All great truths begin as blasphemies."
- George Bernard Shaw
That's often the case.
You have to give props to the casting director.
Looking at the cast now you are blown away by it but besides all the acting talent who played teachers and maybe besides Usher and Elijah Wood from younger cast. None of the rest were known.
This was Josh Harnett breakthrough role, he was only 20 when this came out. Clea Duvall did Can't Hardly Wait and The Faculty the same year. She wasn't a big star after this but a lot of her more well know films came after this. A few years before Fast and Furious canon for Jordana Brewster. Shawn Hatosy it took for many a long year before he had a major break out on TV. And you also got Danny Matterson pre That's 70's show and the scummy stuff he did.
I like this film, it's got a smart script and is well directed. It's better 6.6 rating on IMDB.