Gokusen

At first glance this looks like the female version of GTO. However Kumiko is the daughter of a Yakuza boss and must hide her background so she doesn’t get fired from her first teaching job. Comparisons aside, Gokusen stands in it own right with its witty humour and dialogue.
From Baka-Updates:
Fresh out of college, Kumiko “Yankumi” Yamaguchi becomes a math teacher at an all-boys high school. Unfortunately for her, she’s assigned by the school board as the homeroom teacher for class 2-D, which happens to be the class of delinquent students. When the class attempts to make a living hell out of Yankumi’s career, they fail as her persistence and aggression gain their respect. However, little does anyone in the school know that Yankumi is actually heir to the Kuroda Group – one of Tokyo’s most powerful yakuza clans.
-ANN