The first Catholic school I attended was a small all girls' school, and you are right, they had some pretty wild students. The student body seemed divided into two groups: the ones whose parents sent them there for a good, Catholic education and who took it seriously, and the ones whose parents found themselves with wild girls and sent them to Catholic school "so the nuns could straighten them out." I transferred to a school that was much stricter (though co-ed and about ten times larger). So you are right, you never can tell.
My own goal for my children is for them not to be considered "cool"! That seems to be very important to some parents, and I do think it can be a recipe for disaster.
No, I want nerdy children! Being cool (and the never-ending quest for elusive cool) got me in trouble.