Taken from Matthew's Anime Blog:
Daisuke is a 23 year-old new schoolteacher. He ends up being put in charge of a 3rd grade elementary school class since the previous teacher quit, and in that class there's a girl who's quite a troublemaker--Rin Kokonoe. You could call her a masegaki (used to describe a kid that acts more like an adult in some ways), and she's also part tsundere (though more dere than tsun).
Seven Seas has canceled Kodomo no Jikan's (Nymphet) licensing due to some so-called "disturbing" content. Read about it on Matt's blog.