When does this happen? Afterschool? Is he hungry? Does he need time to just decompress? Or to get out and run around? Not getting enough sleep and needs a nap/rest time?
The key to understanding my child was realizing that he is an introvert and after a day at school he NEEDS downtime where he is just doing something fun/relaxing for a while. He has just spend 6 hours forced to interact with other people. And to realize that he was a growing boy who needed FOOD by 3 in the afternoon. Both of those things help my child.
In addition if he is getting emotional after school, perhaps something is going on during school. Some kids really hold in their emotions at school only to just let go when they get home.
Good Luck. I hope you can figure it out.
