Hi, I'm not even sure when I read it or what scanlation group it was (possible Nakama?)

It was a series of oneshots and this story was only one chapter. I can't remember if it was fully scanlated.

Student doesn't want to study, teacher's the seme and has sex with him.

I'm sorry this is really vague. Thank you very much in advance~!

One of these? http://www.mangaupdates.com/series.html?category=student-teacher%2Brelationship_delinquent%252Fs&genre=Yaoi&perpage=50

I'm sorry. Not on that list 😔

I also tried these too but to no avail - http://www.mangaupdates.com/series.html?category=Delinquent+Uke

It was a cram school, the student was a trouble-maker but the teacher was bulkier. It wasn't bara-like muscular though. Pretty sure it wasn't Uchida Kaoru's delinquents either. The student might have stayed back and gotten private coaching and I vaguely remember them wagering on the student's test scores and the student doing well on it.