I once did a teacher... but she was a elementary school teacher and no I was not a student. I did got cockblocked twice though.
The first one was my history teacher after I graduated from high school. She was drunk, but she had a fiancee at home and shamefully she wasn't that hammered.
The second time was my first university teacher (organizational behaviour). I drew attention on my the first lesson both by being a smart-ass and wise-cracking comments, but also displayed my knowledge. We also had fun discussions online back and forth about both the necessary subjects, but also talked casually. Then when I had the guts to ask her out, she told me it wouldn't be wise at it would be a conflict of interest. The "and what about after the exam" question was never answered...
The Doctor will see you now
Promoting Lesbianism --> 
