I don’t have any experience teaching SEN students but I do have a little experience having them as part of a youth group I have run in the past.
What I found with SEN students is they only listen to people that they feel are close to them and really care about them.
That’s why they behave when their parents are in the room.
I know that you are there to teach him something but in order for him to let you do that you might have to gain his trust first, either in conversation and talking to him about what he likes and spending time getting to know him or sometimes bribing works. Either way it’s probably going to require a bit of time and a lot of patience.
I’m no expert though 🙂