First, the teachers need to build a loving relationship with your son. A child who does not feel lovable and cherished will not care whether an adult teacher "disapproves" of the behavior he uses to express his unhappiness. So the teachers need to make sure that they are giving him enough cuddles and lap time. Observe whether they caress his hair and give admiring comments when they "catch him being good" that is, building a block tower or playing peaceably next to a peer.
Be sure that you read lots of stories about caring and sharing, such as Horton Hatches an Egg and other stories of kindness and generosity (in a simplified way if the story is too long). Remember that learning to feel comfortable sharing and taking turns is a long, slow process for a toddler. Give lots of praise when you invite a playmate over and they are able to share toys or take turns. Be explicit. Tell your son just what you are admiring and how proud you are that he is learning to be such a good playmate, such a good friend.
Model sharing and caring in your household. Show patience by your tone of voice with the other members of your household. Use politeness words with each other. Remind your toddler to say "please" and "thank you" and do not give him a toy when he gives "orders" to adults for what he wants. Show your pleasure that he is getting to act like such a grown-up little fellow.
At the same time, meet your toddler's needs, since he is still so little! Hug him lots, and let him lean against your body as you read daily with him. Teach him that sometimes we need to wait for a turn; sometimes we cannot have just what we want right away. Explain, for example, when it is near supper time, he may want a sweet, and whine or act mad if you deny that to him, but you can give him a slice of cucumber or apple instead which will help him grow strong and healthy. You want him to have a good appetite for his dinner. Then tell him how proud you are that he is learning to wait and keep calm until suppertime. Tell your child the household rule in your family: "No hurting other people!"
Firmness and love and lots of short, sweet, earnest, and specific talk will gradually help your son learn the self-control so he can act by the "be kind to each other" rule .