I would start with doing a kinder duty and then speaking to the teacher about getting him assessed if you still have concerns. There are a couple of children being assessed at our kinder.
I did kinder duty a few weeks back and it was a real eye opener watching the dynamics of the group. While I was there a lady (assessor) came and spent 2 hours with this child which was just playing with them and being right there when they were playing with other children...One minute the child was playing in a dolls house with a couple of other children and in a split second this child had thrown a wooden piece of furniture at another childs face...even the assessor didn't see that coming...things happen so quick!!!
I think organising a playdate with another child at kinder is a great idea!!