Has the school suggested a confernence, it sounds like it would be good if everyone met together and got on the same playing field. I would think other kids have done this behaviour before.
Really could you some more information. What grade is he in and when is his birthday? Did he have these problems in elementary school? You mention his behavior. What about his grades. Are they bad? If so, have they always been bad or when did they start to change. Oh, and was he in a private elementary school or public school. And, any big family changes or moves in the last two years?
When you go to talk to the school. Do listen to what they say, and ask for suggestions. The school should be able to handle the sexual comments. That is not uncommon at this age, and they should be used to dealing with it. Obviously, taking him out of his old school did not help too much. So Its definitely time to try something new, so do listen to the school suggestions. If you feel like answering the above questions, maybe we can give some more help. Hope this helps.
May I ask you could he be watching anything on TV or on the Computer that may have sexual implication,they do usually get it from somewhere very often have heard or seen it.any magazines left around . What does he say when you ask him why he is doing it, I think maybe privileges taken away , with some counseling in mind aswell .