Establish a routine with a specific separation between school time and play times.
School is for learning, playdates/park for fun and play. Invite a friend at home on a specific day of the week.
There are fun-time at school, but they are not the main purpose of school. Become involved in what he does in the classroom, if you have time and the school is keen, become a parent helper.
Last, but quite fundamental: limit screens (iPad, tv, gaming) during the school days. Life on device is fast paced, full of colours , excitement , stimulus, instant rewards (stars, series, compliments), but real life is not. There are empty moments in real life, from waiting for your turn to show your work to the teacher to queuing for lunch or whatever. The brain gets used to a fast rhythm, never an empty second.
Have books instead of screens, read a story together, play a board game, ....