As a respite provider & private tutor, I have a five-year old boy who sounds very similar. He is diagnosed with Atypical autism/PDD, ADHD, and Intermittent Explosive Disorder, among other things.

I would agree with the previous poster, the tantrums may very well have an environmental trigger. They may also been related to a physiological abnormality that has not been addressed with his current medication. Or, not unlikely, there could be a combination of these triggers & an environmental influence. He may have found tantrums to be reinforcing in the past, and as such uses them now to get what he wants. It's quite possible that both physiological and psychological factors are present--which makes it quite difficult when trying to decide what approach to use!

The only solution I have found is consistency. Regardless of what triggers the tantrum (even if there is an obvious environmental trigger) I remove him from the situation and place him in a safe place where he can calm down. This is not done as a punishment, but as a way to ensure the safety (emotional, as well as physical) of the child and the others around him. At one time we were forced to use a locked room as a safe location, as physically restraining him seemed to be both overly intrusive and risky (for him and for us). I would not typically advocate this approach--but with this child I found it vital.

We saw the same problems with this child when he was placed in a mainstream kindergarten, when he was moved to a small group kindergarten (eight children with two teachers) where the environment was less chaotic he did much better.

As far as treating the autism goes, there are dozens of approaches to treating autism that go beyond the scope of this board. I would suggest doing research on the gluten free, casien free diet, chelatin therapy, biomedical approaches, treatment of potential yeast infections, ABA therapy, neurological excersizes, sensory integration techniques, and Greenspan's Floor Time approach, to start with. Unfortunatly, many of these approaches are financially draining, and it is typically impossible to determine what will be effective without actually trying it. I would suggest the book "The Out of Sync Child" and the accompanying book "The Out of Sync Child has Fun" as resources that you, as a care provider, may find useful.