maybe this? it's great btw so read it even if it's not what you had in mind http://www.mangago.zone/read-manga/oresama_teacher/
A girl, Teacher right?
no, but still a great one. read it after your recommendation
male teacher
Owww
Mamotte Agemasu (I am very sure this is the manga you are talking about)
I feel as though ive read something very similar to this manga. it was about a girl transferring into an all boys school lead by a violent student and his gang. the heroine falls for the gang leader and they keep trying to be romantic or get it on but the leaders gang keeps cock blocking them. Anybody know it?