medaka_no_gakkou
A gag 4-koma manga about a girl named Medaka who enrolls in a school that will let anyone in so long as they're literate.
Manga: http://www.mangaupdates.com/series.html?id=14601
An OAV was adapted from the manga in 2004: http://www.animenewsnetwork.com/encyclopedia/anime.php?id=9417