ok i know allot about this because i ahve a son with autism and my friend also has one with autism ,mine is 8 almost 9 and he goes to the toilet in the day time but at night time he just soils himself or even does poos and sit there in his own thilth and dont say a thing,and my friend her son is 16 and does the same .

your son can still go to pre school but he will need a carer his own teacher to take him to the toilet and to change his nappy while he is adjusting .

i to have tried rewards and stickers,everything i even painted my toilet into an under the sea theme.

the  one thing that you can do and that works  is not to ask is he wants to go to the loo but tell him to go.

my son will sick and bounce up and down and holds his bladder and then gets a gut ache,every hour on the hour take him to the toilet ,or every 2 hours get a magazine or book,or a game if he like to play games stick some posters on the wall so he dont get bored ,make the toilet appeling and tell him he has to go to the loo or he gets a tummy ache and gets sick,sit him in the loo and give him 5-10 minutes adn make sure he tries to do something if he has done nothing give it half an hour and try again specially if its been a few hours since he has used the loo.

at night time its a bit harder unless your prepared to wake up every 3 hours to take him to the loo.having pull ups is a good clean option for bedtime only ,and dont give him anything to drink once he is in bed .

1 glass of milk or water 30 minutes prior is ok and make sure you take him to the loo prior going to bed .

i ahve had a few dry nights this way.

there isent much else you can do.but keep taking them to the loo regular,if you ask them they will just keep telling no they dont need to ,only to go in their pants withing an hour of you asking .

Try Tom's Toileting Triumph DVD.  I look after an autistic child and this worked wonders for his mother when she was TT him. It also worked on his siblings.