Hmm, how old is your son? I think he is just shy and doesn't want to speak only when he wants to. My son is 3 yr old, he can speak very well and if he don't know who those people, he won't speak because he was shy and not comfortable, didn't want to speak because he don't know who that person or whatever until he feels comfortable around them then he'd speak. He just started school last Jan. 5th, he enrolled at Head Start. I asked them how my son is doing at school, etc..Teacher said he have spoken some words and sign language as well now he has been talking more since he now feels more comfortable at school and has made some new friends. He really loves going to school and look forward to it to ride in the bus and go to school. So, I'm glad all worked out good. I think you would probably need to attend his school, tell your son to talk to them, make him feel comfortable, etc.