i agree with the others, my ASD son is on the lower functioning side & he will be 11 this year. he just decided a couple months ago to start using the toilet every day. you can't force it....its one of the very few things they have control over. so sorry for your frustration. but look on the bright side he could be using the poop to smear all over himself & the walls in his bedroom. ( my son when he was 3-5 years old) I was complaining about it at the time online to a support group & a women came on & said "look on the bright side at least he's not eating his poop like my son is" yeah i'm telling ya I did feel extremely greatful that it wasn't that bad. it was still really, really hard but there was always that other thing that I knew I didn't have to deal with & that was a peaceful feeling. good luck hun....its a long haul so sit back & have a drink!

I know you probably don't want to hear this, but he simply may not be ready. Our son is six years old, and we still have issues with potty training. Just use the little potty if that's what works. I have a friend who had one in the car for use when they were out and about. Have you also tried the potty seats that fill in the gap a bit? My son liked the Bumbo potty seat because it was squishy but felt very stable.

Is he showing signs of being ready to train? My son was just about 4 when he would bring me diapers so I could change him. If he is showing signs then it's time. It is not going to be easy. Lot's of kids with autism never learn to use the toilet. I'm lucky. Out of four kids he was the easiest one to train.

No more diapers or pull ups. Period. Pull ups are a waste of money. I went straight to underpants. Make sure you buy lots. If you've never used PECS now is the time to introduce them. A life safer. My son refused to sit on the new potty chairs that are plastic. I found an old fashioned style potty chair that looked just like a childs seat except for a hole in the seat. A bowl was placed under it. I am putting a list at the bottom of my post of the books and DVD (it was VHS when training my son!) that I bought that were helpful.

Make sure you have time to devote to this. You really need to be house bound for a few days. I gave Jonathan drinks and when he would start to pee I would whisk him to his toilet and sit him on it. I would then sit on my toilet. We would go together. Honestly once Jonathan realized what his toilet was for he never had an accident. Training him took 2 weeks. My other kids not so easy but I think that two factors worked in Jonathan's favor 1. He was 4 and 2. His sensory issues. He HATED wearing wet undies.

http://www.gcwoodworks.com/Potty%20Chair%20Wood...

Toilet Training for Individuals with Autism or Other Developmental Issues: Second Edition

Once Upon a Potty -- Boy

Once Upon a Potty for Him DVD

Standing to pee in the little potty might be a little messy at first but eventually you can put the little bucket from the little potty in the big potty to help him transition until he's not scared anymore.

I am having the same prioblem. My son has the motor planning part down. He cones in takes off his pants, sits, flushes, washes hiss hands. The whole shebang. But he won't "go" On the potty. He will sit there for 15 minutes (with his iPad) and then get down and do his business. My husband suggested that I try teaching him to pee standing up since that's what he's going to do anyway. I'm going to try that. Who knows maybe that could help your little man too.
Good luck! It's not easy. Everyone says just stick with it but it's so hard. I guess it's only a matter of time before it clicks for them. Keep us posted on your hard work.