What the hell is it?

I'm trying to find this doujin about a guy who comes to an all girls school as a teacher or some other kind of staff member and starts having sex with the students. This one popular girl is particularly disgusted by him and the groups of girls that look up to her agree, until they all get fucked by him. Eventually he gets her to have sex with him.
Can anybody tell me what this is? I'm been driving myself crazy trying to find it.