FWIW, my own experience says its not uncommon for teachers to come on to their students. In my high school, I know one teacher for sure who was doing this. I was rather oblivious to the goings-on, but my high school BF and my father both alerted me to stay out of this particular teacher's office. They simply didn't like him. I guess guys have a sense for this kind of thing. It wasn't until he got one of the students pregnant that he was fired in disgrace. Oh and he was married with a very pretty wife and young daughter. Looking back on it as an adult I can see the signs. He was actually very manic (which the girls interpreted as 'charismatic') and just a tad too familiar with certain of the students, who I suspect had various vulnerabilities he exploited.
In college, its even more common. I suppose b/c its legal. CAM knows. Its relatively common for advisors to date their students. I even know someone who married his.
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh