It has to be I My Me Strawberry Eggs! It's my favorite student-teacher romance anime.
They are such a wonderful pair. A long-haired, feminine guy and short-haired tomboyish girl. What an interesting combination.
I wish the anime would be at least 26 episodes so their relationship will be explored and deepened in no time.
EDIT: Hibiki is a real teacher who cared a lot for his students, and he never tried to make any advances with his female students nor took advantage of their vulnerabilities, although in Fuuko's case, Hibiki made a great deal of effort holding back his feelings for Fuuko.
But that was his honest feelings, not lust and he was trying to deny his feelings to the point of lying to himself but in the end, he gradually realized he liked Fuuko, even though he knew it was wrong. At least He cared for Fuuko enough that he encouraged her to try her best.
NEW EDIT: Encouraging/inspiring/motivating young people to think independently and do their best on their own terms is what a true teacher is about.