When your son comes home each day, give him some room to expel some of that pent up energy. Take him to a park, let him ride his bike, and later on, talk to him about the good parts of his day. Talk about it with enthusiasm. You may also want to assess whether he is making friends. If he feels isolated at school, he may be reacting to that.
First graders are very social beings.
Lack of close friendships can cause extreme distress. If he is feeling isolated, make a playdate for a Saturday or Sunday afternoon. Weekends are great times for developing friendships, mostly because on weekends, kids have had a good night's sleep, are willing to play well together, and can manage one on one playtimes better than they manage a group of children all at one time. On weekdays, make sure your son has gotten enough sleep. When you wake him in the morning, wake him with enough time to sit quietly for a good healthful breakfast, and then slowly get dressed and head to school.