I don't have a answer but you are not alone. My son just finished his second year of ESE preschool and will start kindergarten in Aug. He has been pee trained for a year and a half but still is not poop trained. He has not pooped in the pooty for the 2 years of preschool. He still prefers to poop his pants but is you catch him in time you can walk him to the potty and he will go. He was approved for ESY do we will see his he does over the summer. He was only at preschool for 2.5 hours a day do he would wait. Good luck!

I am going through the same thing with my 5yr old and I cant find anything to work with him, my older son was 7 before he potty trained. Both have ASD

well my son has low functioning autism (just in the past year has he made improvement in not being so severe) he is 10 & it finally looks like he might be fully potty trained I don't want to count my chickens or anything but ive been changing diapers for a total of 12 years & i'd really like to see the light at the end of the tunnel (I have another child who has delays he has many health problems though)
Honestly ive tried a million different things but bottom line if he doesn't want to it's not going to happen, its really one of the very few things he has power over. good luck hun....all autistic children are different you could start by making him change his own pullup (if you don't already do that) (personally found the most helpful thing is giving him step by step picture instructions on what needs to be done. I have painted on our walls step by step instructions & point to each one. (it doesn't hurt to also pretend to do the same thing as your pointing to)