boy in her yr had said he was 'going to rape her' because he liked her and she told him she wasn't interested in him!!!!
If he's equating rape with sex - well, he's saying he'd do it because he likes her, but it's not reciprocated. Sounds like he understands what rape is to me. And even if he thinks it's like beating someone up - that's not okay, either.
Someone needs to explain consent to him. Unless they both want it, it shouldn't happen. He needs to learn that if someone says no, no means no, whether he wants a different answer or not.
I'm assuming that they are too young for it to be more than words, but even if he tried to kiss her against her will, that's not okay, either. Nor would be hitting her.
I'm not quite sure where being a slower learner comes into it. But I guess you have to leave it with the school for a few days to see what action they take. As an individual, he can be dealt with. I would be more concerned about it being a normal thing to be said around school. If it were my school, I would want something done to try and change that, too, to try and get some understandin of why it's not acceptable.