Sex=Love^2

From ShoujoMagic: All Kumiko wants is to become a teacher; however her father is dead set against it. He is giving her one chance to prove herself as a teacher before forbidding her from pursuing this career forever. Meet her newest student, Ryu-kun. He has NO desire to LEARN anything from his tutors, rather he is an expert at teaching THEM about...SEX?! Note: The story was originally released as a single short story, but it later became a series.