Based on the seinen manga by Watashiya Kaworu, serialised in Comic High!. NOT related to the other Kodomo no Jikan by Goto Akira!

It`s the cute ones you`ve gotta watch out for...

23-year old school teacher Aoki Daisuke has a huge problem. One of his precocious 3rd Grade students, Nokonoe Rin, has the hots for him?! Yes, mischievous Rin has proclaimed herself to be Daisuke-sensei`s girlfriend and is now on a warpath to win him over or cause him to lose his job...whichever comes first!
Besides Rin, Daisuke`s got other problems to take care of -- one of the students in his class, Mimi (one of Rin`s friends), hasn`t been attending school recently.

sauce
http://anidb.info/perl-bin/animedb.pl?show=anime&aid=5029
(by Watashiya Kaworu)

http://anidb.info/perl-bin/animedb.pl?show=anime&aid=2001
(by Goto Akira)
WINNNNNNN!!!!!!!!!!!!!!!1