Today, my DS calmly guided a toddler to the top of a playground slide and then deliberately shoved him down it. Fortunately the Toddler was fine (if shaken), but when I sat DS down and talked to him about what he'd just done, he told me matter-of-factly that he hadn't wanted this child on the playground. Despite our chat, he shoved a different toddler (much less dramatically) a couple of times more before I took him away.
I'd love to say that this was an isolated incident, but at playgrounds and in a playschool class he hits and shoves on a pretty regular basis. It seems mostly tied to sharing and sense of space issues - either not wanting to share a favourite toy (or playground in this case), or someone getting too close to his personal space. He often seems worse if he's not eaten, but that's not the problem in pre-school at least.
He's a very large 3 yr old, and could really do a lot of damage.
He has an older sister who is quite bossy and can be aggressive with him, although she's well behaved and considerate with all other kids.
He does seem to be making some progress with one preschool teacher, with a small pupil to teacher ratio.
We've tried time outs, sitting him down after each incident and talking about it, praising gentle behaviour, etc.
We are really frustrated with the whole situation, and would welcome suggestions of anything new to try. Does he need therapy (at 3?)?