Thanks for the advice.. My son can speak just fine for his age because his dad is hearing and he sees his grandparents (my parents) often and they all speak to him and he can speak on his age level. I think it's probably what you said. Fears of strangers. Ever since he was a baby he refused to let anyone touch him except for me, his dad, his grandparents. That was it. I had a hard time getting a babysitter because he would freak out. It took my bestfriend a long time to get closer to my son. When my daughter was born, he would freak out if anyone holds her. He would get really mad if a stranger held her. He will speak with other kids IF he hangs out with them long enough to know them well enough. When he wants to join an activity, I would sign him up but when we show up, he would freak out because there's usually too many kids. Now I realize that is probably his problem and I will bring it up to his teacher and see if she has any suggestions and I will definitely suggest that reward idea to her. See if it would help him break the ice.
I do know he doesn't hate his teacher. He tells me that he likes her and he smiles when he sees her. I think maybe it's just the large crowd of kids.