Potty training a special needs child

My son is 5 1/2 years old. I started potty training him at the age of 2. At that time,  he showed all the signs of readiness. I started to feel that something was not quite right around the age of 3. His pediatrician referred me to a neurologist and at age 4, he was officially diagnosed with SPD, Dyspraxia, (Mild) OCD, ADHD and (Mild) Motor Tics. Prior to his diagnosis, I did everything by the book. However, since he has been diagnosed, I have struggled with determining if his potty resistance is behavioral or due to the neurological issues. I've done extensive research regarding potty training and I am aware that a delay in potty training is common with SPD children. But, his actions lead me to believe that he is just being stubborn. Here are some examples/specifics of his behaviors:

- He does not wet the bed at night.
- Nothing seems to phase him; he has come home from school upset because kids have picked on him, then he'll poop/pee his pants 10 minutes later. I have tried rewards, praise, charts, games... he will get upset if he doesn't get a reward, but 10 minutes later, he's pooped/peed his pants.
- After years of potty training, I can recognize the signs of an oncoming BM (i.e. facial grimacing, body posture, crossing of the legs) When I see these signs, I ask him to go to the bathroom and he insists that he does not have to go. 10 minutes later, he has pooped his pants.
- He does not tell me when he has to go or when he has gone in his pants. Ex: A couple of days ago, he was in his room playing and I checked in on him. As soon as I walked in I smelled it. I asked him if he had pooped and without hesitation, he looked at the poop on the floor. (He was wearing boxers that day) He knew that he had pooped on the floor, yet did nothing.
- He witholds his stools to the point that his butt hurts so bad he can't sit. He's was checked by a gastroentologist about a year ago. A physical examination and xrays determined everything was normal. He was given a stool softener, which didn't help. After months of no progress, I stopped giving it to him for fear of him becoming dependent on it.

I've realized that all of these behaviors happen when he is playing. After the "poop on the floor" incident, I asked him why he didn't come tell me that he had pooped on the floor and he said "Because I didn't want to stop playing." He's told me this many times. I've tried to help him understand that playtime is wasted when he goes in his pants because he has to clean himself up, change his clothes, etc. He's scared he's going to miss out on something.

We put him in underwear when he was about 3. At one point, a child psychologist (yes, I tried that, too!) instructed us to put him back in pull-ups. I don't remember when or why we went back to underwear but he hasn't worn a pull up in almost two years (except when we go swimming).

I have literally tried everything. He reached all of his milestones at the appropriate ages and speech development was normal. He is extremely intelligent. Currently, he is in a regular kindergarten class in a public school. He is picked on now and I know it may get worse as he moves on to the 1st grade. He already has a lack of self-esteem. He was kicked out of his daycare when he was 4 because he wasn't potty trained. I quit my job about 4 months before he started kindergarten to try and get a handle on this. And now, I sense the teacher is becoming less tolerant. I don't know what else to do. Should I put him back in pull-ups? Should I try a different reward system? Is it okay for me to make him go to the bathroom when I know he has to go but insists that he doesn't need to go? How can I get him to understand that its just easier to go to the bathroom and that it takes up more of his playtime when he goes in his pants? WHAT SHOULD I DO?
Please help!

[crabby70]

Does he go at a certain time....This way you can insist that he stay on the potty till he goes....My daighter has CP she does go on the potty with assistance....Most of the time she is in daipers...She has started being mainstreamed so I got a routine with her so she doesn't go in the regular school...I would not let him play till he made it...rewards anything I would just keep trying.....Maybe an older cousin he likes to play with or someone that he looks up to could tell him he wants to make poop in the potty....Best of luck