Thanks guys.
He had another outburst today and my wife picked him up early. We're keeping him home the rest of the week, since his problems have been daily.
I suspect that there might be some teasing or less overt bullying going on though the teachers might not be aware of it. He is a quirky kid, not interested in sports (a sin for a boy of that age) and loves math and science. I would not be surprised if he is a target.
Also, he is very sensitive, so even if the teasing is just a few snickers in the hallway, that might be enough to set him off. And once the other kids realize that he can be provoked, there will be no end to it.
The teachers swear that they are not aware of bullying or teasing but I cannot imagine that they see everything.
Nonetheless, tonight he is in good spirits and seems cooperative, though distracted as usual.
Hopefully, we'll figure this out soon.
