Hoping someone here can help. I'm new to this section of MN.
DS1 (5) is almost certainly on the autistic spectrum, probably Aspergers, from the books I've read and diagnostic criteria I've seen etc. In the process of being assessed, although paed is reluctant to make any kind of diagnosis until he's been in his new school a year, even though most of the professionals we've seen are fairly confident he has Aspergers. He started this school in January - first school was a private school and a complete disaster, this one seems infinitely better, they have a much more positive attitude and are determined to make it work and not to fail him, which is fab.
However, now that he's settled in, his behaviour seems to have got worse and worse rather than improving as he's found his feet. He has lots of obsessive behaviours, which they were aware of. The teacher is doing her best to minimise these as some of them are disruptive to other children/ the general routine or even the safety of other children (eg. he has recently become obsessed with the tyres in the playground and tries to stack them up really precariously when they are arranged on the ground for an activity). The obsessiveness is all probably part and parcel of ASD. He flips very easily at the smallest things, reactions are completely disproportionate to the problem.
However, the thing they are struggling the most with is just persuading him to do things he doesn't want to, eg R-Time, picking a reading book (no idea why, he is a fantastic reader with a very high reading age), doing appropriate maths work (again, he is great with numbers but will randomly refuse to do the things which are set and want something easier, but then if given the easy stuff will act up because he isn't being stimulated. After Easter, he will be doing maths with Yr 2 - currently goes up to Yr1 3 times a week for numeracy but is way ahead of them too).
Consequences and rewards seem to have no effect on his behaviour and I honestly don't know how much of it is down to his SN and how much is just down to him being utterly stubborn and wilful! He's so adamant he has to be in control all the time. Even when he needs the toilet he will put it off because he wants to keep doing his activity of choice, if anyone reminds him or asks him to go he will refuse on principle and frequently wet or even soil himself rather than admit that I/his teacher was right. 
I really need strategies to deal with this, both for me to use at home and to help his teacher at school. I know we will probably always need to make allowances in certain areas but he still needs to learn that he has to cooperate with his teacher. Am at my wits' end! Sorry for the long first post!