Its call Magister Negi Magi and this is the story outline from what I heard.
The protagonist is a 10 year old boy that knows magic. He is send to a high school posing as a teacher to study magic secretly. And guess what, the lucky dude has 30 students in his class, all very pretty girls. Pretty standard Akamatsu fair if you ask me...
IIRC, the chinese translations is at book 2 already.
