I work on a campus literary magazine called Small Craft Warnings. It's one of many on campus: there's a magazine for Spanish-language poetry, one devoted to writing by Asian students, one for writing by black students, one for women-writers only, one centered on the idea of diversity, one for academic writing, one for science fiction, one for humor writing, and there's probably more that I don't know about.
Small Craft Warnings is the only magazine that is all-inclusive: we accept submissions of all kinds (artwork, short stories, poetry, personal essays, plays, etc.) from all members of the Swarthmore community (that is, faculty and staff as well as students.) We usually get about 100 submissions from 60 different people (many people submit more than one piece, but we will only print 3 pieces by one person in any given issue.) We usually accept about half of the submissions we get, so it's selective but not that selective. The editorial board is composed of 12 students who read submissions anonymously and vote in the ones the majority of us like. An issue of SCW is published each semester and 500 free copies of the book are distributed around campus.
The quality of the submissions pool as a whole determines the quality of the magazine as a whole. Frankly, SCW not always full of amazing writing, but there's usually a few pieces that are exceptionally good. It's certainly a better (and more sophisticated and visually pleasing) than any high-school literary magazine I've ever seen.