When Mary went to a pre-primary impaired class, she was still having pee and poop accidents. As many of you know, she is autistic and also had mild brain damage at birth.We didn’t realize she had developmental disabilities at the time, so I thought I was an awful parent because I was not successful in one of the major tasks of parenting.
Our (un)helpful doctor suggested she would be potty trained by college…And he was right. She was potty trained by the time she went to (and graduated from) college.
Two things helped us:
1) We stumbled upon something that motivated her. She was very excited by the task of dropping pennies into a giant plastic bear bank that my father found at a garage sale. If you are having similar issues, may something serendipitously occur to you. Praise, stickers, celebrations, etc., were useless.
2) Motor training, which we found in an old book, Toilet Training Without Tears, was helpful. It is still available on Amazon. http://www.amazon.com/Toilet-Training-Without-Charles-Schaefer/dp/0451192125. This book listed several methods. The one that was effective involved motor training. Every time Mary had an accident, we would go through all the motions of going potty. Go to the bathroom, pull down your pants, sit on the commode (by the time she was five, she was big enough), pull up your pants, etc. 10 times, each time. It took up a lot of my time, but after a couple of weeks, she was not happy about having to spend so much of her play time going through the motions. And each time she was successful, well, there were five pennies for the bear bank.
annkilter 
These are very good tips. Potty training children with autism can be extremely challenging. My son was very late in the #2 department. After years and years of him terrified of the toilet, struggling with him, bribing him with toys and doing every other thing we could think of, we finally found something that worked.
I had him look on a website and choose anything on the site he wanted, within reason. He picked a big remote control truck. We printed out multiple pictures of it and posted it all around the house, including the wall right next to the toilet. Within 3 days he was taking care of #2! The first time ever in 8 years! It was a huge milestone and such a relief.
That’s the thing about our children…some things just take years and years. And then suddenly, something works, something clicks, a switch is thrown. And it is such a relief.