Why can't religious students have clubs at schools?

[Charlie Brown]

I just don't see why not. If all the school does is allow students to use a classroom after/before hours and have the same resources that all clubs have, then what's the problem? Surely an impartial observer would not see that as "endsorsement" or any special favoritism (as per the conditions of O'Connor's "lemon test").

I'm not talking about "hate groups" like Phelps and Co., or the KKK, just average religious students who want to meet and talk about faith outside of school hours. That doesn't seem to be asking for very much.

On edit: I know religius clubs do meet, and are considered legal. I've just read a lot of posts, particularly in the Obama threads, that say they are not legal. I'd just like to get a better grasp of the issue.