preschool pickups

Today, I picked up N from preschool. He and about 6 other kids were sitting around a table, eating snack. I asked N how his day was. N tells me a story which I could understand only parts of: he was playing outside and ended up pushing some other kid. So, I said something like: Pushing is not nice. We need to practice using our words and keeping our body to ourselves. Words can be powerful.
Then, another kid says: N pushed me today. And I responded sympathetically. Another kid says: N pushed me twice. A third kid says: N pushed me too. This continues for a while and finally another child says: N tried to choke me today.
Did I mention that this was in front of two other parents?
I can understand that the chorus of 'N pushed me' may have been the result of kids wanting to be part of the conversation. However, the addition of the choking comment is no laughing matter and I do not doubt that it happened.
We just don't know what to do with this kid. My search for a nanny is fruitless so far. I wish that a book would fall from Heaven with all the answers and a magical index that automatically opens to the page I need.
We work so hard and spend so much time thinking about how to 'deal' with N and his behavior, how to teach him, how to provide positive encouragement, etc... . N is making progress, but it is painfully slow. It's really hard to celebrate the progress he has made in light of the path he has yet to travel.