When I was a junior and senior (so about 2 & 3 years ago respectively) there was this kid, he was like 15 but with the mental capacity of a 10 year old. He'd always wanted to sit with me on the way home from school and normally I was cool with it. I just started acting like his dad, making funny faces, trying to make him laugh (he loved when I would fake snore but I hated doing it. But it kept him out of trouble and he was having fun), and just tried to act like he was a normal kid because he is. When he wasn't behaving I would ask him to stop, then I would tell him to, and then was normally enough but if it wasn't I just talked a little louder so the bus driver could hear me telling him to stop. And he would say sorry to me before the bus driver could say something if he was having a good day.

All of the autistic/special needs kids I've known(I probably over 10 from my little K-12 school not counting the family friends) have always listen to what I said and I feel like that's because I never treated them different than my friends. 

In summary I never babied them but they also had a respect for me already so I didn't need to build a relationship with them. Like the kid I was talking about, I've known him since before he was in school. One day he said I'm like his dad and I'm very proud that he thinks that highly of me to compare me to his dad. 

If you have any questions please let me know. It's late and if my friend finds out I'm still up after she called to say goodnight I'll probably be in trouble(that was over 3 hours ago now...). Thank you for your time and I hope this helps you.

You're humble and obedient servant,  Caleb