My son was diagnosed with ADHD at the young age of 7, he was very sexually active in his head which is from what I gather fairly common in ADHD kids so I am not shocked at his sexual comment.

Also my son would of taken an age to get the message that he was not wanted.

This is not making life for your daughter easy and its not fair I am sorry that she is having to go through this but perhaps you can explain the ADHD factor to her and she will have to be consistant with her no's and if this does not work maybe a word in the teachers ear if only to make her / him aware of the situation.

Hugs to you both.