there was this yaoi where a student (seme) was blowing his teacher during lessons, does an...

http://www.mangago.me/read-manga/only_you_tohjoh_asami/tr/94054/page/169/ (the story starts at page 161)

there`s another yaoi with a similar scene, just that the positions are reversed: http://www.mangago.me/read-manga/oresama_wa_koi_no_dorei/tr/85845/page/170/ (the story starts page 7-41 +169-176)

for more student x teacher yaoi check out my list:
http://www.mangago.me/home/mangalist/7548/