A boy once came to the Chazon Ish and asked if it is proper for him to pursue a shidduch with a girl who went to a more "modern" school [this was in 1952 and there was no local Beis Yaakov for her to attend].
The Chazon Ish answered "Are you marrying the school or the girl?"
This works two ways. Just because a boy or girl goes to a good school doesn't mean that they are so terrific themselves. The Mir has good guys and the Mir has more "bummy" guys. Michlala produces great girls and they also produce girls of a lesser quality [not that I have ever met one but that is the reality...:-)]. Judge a person more for who they are. The school they attended is just one small piece of the puzzle.
I know a chasidish guy [hat, beard, gartel, the works] who in his innocent youth attended Camp Lavi. He wouldn't go back there but he feels that it didn't affect him too terribly in the long run....