So... I have no clue if this is relevant or not. Considering the comment about the short stint in preschool it might be...
At that age a child who is feeling overwhelmed in his/her environment, and especially with (harder to predict) peers, especially during unstructured time, might react by making sure said peers back off. A surefire way to make other kids back off and leave you alone is to hurt them (possibly preemptively). It is a maladaptive behavior. But it works, and all the lecturing about rules and most of the usual consequences (starting with time outs!) will not work as long as they get what they were looking for (more space and less anxiety).
Working on identifying triggers and teaching the child how to 1) figure out they are getting overwhelmed and 2) extract themselves from the situation before they blow up is the only way to fix the problem. This needs to be explicitly taught (and scaffolded).
Also +1 on both "see both instructional level and behavioral expectations worked on at the same time (but not linked as a reward/consequence)" and "This doesn't have to be done *instead* of meeting his other learning needs."
