I'm not sure cuz there aren't that many sex scenes in this one and it's been a "long" time since I've read it but I think the teacher is the uke in this one? And it's kinda popular so you probably read it already.
http://www.mangago.me/read-manga/yukidoke_no_koi/
sorry if this didn't really help .-.
also, i love your username and pfp
This one is a favourite of mine. The art is gorgeous http://www.mangago.me/read-manga/oni_ni_hatsujou/
http://www.mangago.me/read-manga/goodbye_lilac/
one of my favorites
any bl that has seme student x uke teacher ?? if there's a list it would be great too (๑•ㅂ•)و✧