I know this is an old post but thought I'd coment as I've just experienced this. I'm
In college and been self harming for around 3 years, I've never told anyone however I slipped up yesterday and managed to roll my sleeves up briefly in front of my teacher. I was amazed at how nice she was, she quietly asked me if I would go into another room to talk to her but didn't have to if I didn't wanted. She then just talked to me, asked me how was and said that she's always there for me to talk to, I was also surprised when she didn't tell me what she thought as such. I know this sounds stupid but she didn't give me this lecture on how I shouldn't do it and I should find alternative ways but just said to be careful and make sure I keep the wounds clean and that when I'm ready if I want help to try and stop she's there and can get help. She doesn't treat me any differently now and if anything it's kind of a relief that someone knows and is there to talk to. Personally my teacher didn't tell anyone else, I wouldn't worry about that. That's my personal experience anyway hope it helped any one concerned x oh and if your worried about telling a teacher you can always say hypertheticaly and pretend it's someone you know, the chances are they will know it's you but they then can't realy say anything to anyone as they don't have proof.