Without being there, it is hard to know exactly what is going on. Has your DD been specific with you about what the boy is saying or doing? I have found that with my 16 y-o DD, once a boy behaved horribly inappropriately on the bus towards her and other girls, that she tended to interpret every interaction through that filter. Last year she said a boy was bothering her and it turns out he said hello. My point is that the boy may or may not really be doing anything wrong. Your DD's previous experiences could be causing her to overreact. However, the fact that your DD is distressed is enough that the teachers should make it stop. I think if necessary the phrase sexual harrassment will go a long way.

Good luck.

GM
St. Augustine: "Since you cannot do good to all, you are to pay special attention to those who, by accidents of time, or place, or circumstance, are brought into closer connection with you."