Apparently it was a real pool, even back then (or at least, back when the movie was made).

http://www.imdb.com/title/tt0038650/trivia [imdb.com]

"The gym floor that opens up to reveal a swimming pool was real and was located at Beverly Hills High School in Los Angeles."

The two key words in that sentence: Beverly Hills. Bedford Falls? Probably not so much.

I always just figured that it was the 20s and that public schools had tons of moneys since they were funded through raccoon coats and bootlegging.

In the 60th Anniversay Edition DVD, there are a lot of explanations to how and why Frank Capra did what he did with the movie including the pool and what Bedford Falls acually is (not a real town, but an extremely large movie set). Pretty interesting stuff.

I think we've learned a lesson here. It is don't rant to a bunch of people about how something doesn't exist just because you haven't heard of it. Unless your sure it really doesn't exist.

Now excuse me while I go rant about how I've never met anybody with a talking duck for a pet in a comic strip.