Are there still boarding schools like this?

Obviously, there are quite a few boarding schools still around, though the bulk of the all-boys ones have gone coed in the years since the movie was set: some by combining with an all-girls school, some simply by beginning to admit female students. Graduates of boarding schools are quite common within a certain subset of American society - basically the same one where graduates of highly prestigious colleges are common.

It doesn't take a lot of work to discover what all-boys schools are left. Here's one list:
http://www.boardingschoolreview.com/all-boys-boarding-schools.php

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I went to an All-Boys catholic High school and might as well have been a Welton-like boarding school. Corduroy suit jackets (I had the patches on my sleeves!), constant hair length checks (could not be over the collar), theology classes with heavy anti-abortion curriculum. Really not that bad, but looking back, I wish I would have went to public school. Last I heard tuition at my alma mater was about $7k per year!(it was under 2k when I attended) ...and still no females, but they did go to preppy sweaters and got rid of the suit jackets.

I went to a bording school when i was a kid a they used to lash me and beat me to a pulp sometimes , it was one of the scariest experience of my life , they also tried to sexually abuse me.
One night i decided to escape and never to set foot in that hell again.

Of course there are prep schools. Prep schools will never die. On the other hand, the clueless OP will

Half the guys at my college went to prep school.