Meet with his teacher one on one. Explain what you are seeing. I have a 7 yo and has been left out before. Then I got pissed and requested meetings. meetings with each teacher he had – gym, art, primary teacher, etc. His music teacher failed him in 1st grade music. Once I started one on one meetings, everything changed. I check in with them every so often, his primary teacher once a month if not more.
I feel like we are on the right track now. He has an IEP and the teachers are more understanding. Take the bull by the horns and advocate for your child, which I am sure you are, but maybe be more forceful. The meetings helped a great deal. I wish you luck. It is heartbreaking…. we are now in 2nd grade and fine tuning medications….