Help with Asperger's son aggressive and defiant behaviour

"The meltdowns and defiance is mostly triggered by refusal to cooperate" - I suppose the place to start is: what sort of things are you asking him to do?
I'm asking because it's possible that the reason he is so resistant is that there are some sort of sensory issues making it impossible for him to carry out some tasks comfortably. Hypersensitivity to certain stimuli comes with the condition, so e.g. if you're asking him to go into a certain room and to your son that that room is too loud, or too bright, or has a particularly unpleasant carpet texture, you might encounter serious resistance even though in your mind (not experiencing the stimuli in the same way) it's a very simple thing you've asked him to do. 

Many people with aspergers are very averse to confrontation, so that in itself could be a problem. Have you tried a behaviour management system that is more reward than sanction based? It would have to be something tangible- say a sticker chart (I used to react very well to stickers at that age) and when he gets X amount he gets a reward (a trip, or a toy or a book- if he has a particular topic of interest you could base it around that?). You would have to explain clearly what he gets a sticker for and be consistent with it. Consistency is very important.

The meltdowns are also kind of part of the territory. There comes a point when external stimulus gets too much and the autistic brain literally can't process it, so it comes out in an explosion of emotion. In my experience there's very little point trying to stop a meltdown once it's started. 
That said, I find pressure helps calm me down more quickly or prevent one when it's close to happening- see if he will wrap himself in a blanket when things get too much. This has the bonus side-effect of keeping him safe from hurting himself lashing out. 

He's more compliant and quieter when it subsides because he's emotionally and physically exhausted. It's THE most draining thing to experience.

Sure a mod will pop in at some point to direct you to the most useful pages of the NAS website. Also who diagnosed your son? They should be able to put you in contact with sources of support if you need them.

"The meltdowns and defiance is mostly triggered by refusal to cooperate" - I suppose the place to start is: what sort of things are you asking him to do?
I'm asking because it's possible that the reason he is so resistant is that there are some sort of sensory issues making it impossible for him to carry out some tasks comfortably. Hypersensitivity to certain stimuli comes with the condition, so e.g. if you're asking him to go into a certain room and to your son that that room is too loud, or too bright, or has a particularly unpleasant carpet texture, you might encounter serious resistance even though in your mind (not experiencing the stimuli in the same way) it's a very simple thing you've asked him to do. 

Many people with aspergers are very averse to confrontation, so that in itself could be a problem. Have you tried a behaviour management system that is more reward than sanction based? It would have to be something tangible- say a sticker chart (I used to react very well to stickers at that age) and when he gets X amount he gets a reward (a trip, or a toy or a book- if he has a particular topic of interest you could base it around that?). You would have to explain clearly what he gets a sticker for and be consistent with it. Consistency is very important.

The meltdowns are also kind of part of the territory. There comes a point when external stimulus gets too much and the autistic brain literally can't process it, so it comes out in an explosion of emotion. In my experience there's very little point trying to stop a meltdown once it's started. 
That said, I find pressure helps calm me down more quickly or prevent one when it's close to happening- see if he will wrap himself in a blanket when things get too much. This has the bonus side-effect of keeping him safe from hurting himself lashing out. 

He's more compliant and quieter when it subsides because he's emotionally and physically exhausted. It's THE most draining thing to experience.

Sure a mod will pop in at some point to direct you to the most useful pages of the NAS website. Also who diagnosed your son? They should be able to put you in contact with sources of support if you need them.

Hi Emma,

Thank you for your message, some really helpful things in there. The sort of things we ask him to do are standard things like, "time to turn off the telly and come up for your bath" "time for bed" . He will just say, " I won't, not doing it" and there is nothing we can do or say to get him to come up. We've tried stickers in the past and he could not care less. But it's worth trying again. Punishment definitely doesn't work, neither do ultimatums or bribery. So coming up with some sort of reward system is probably the best bet.

The wrapping up in a blanket is a good idea, but how do I get him to do that once he's already having the meltdown?

CAHMS diagnosed him, so I will give them a call to see what they suggest.

Thank you again