3yr old son not talking at preschool

hi
my 3 yr old is very talkative and talk very well at home , when we take him shopping etc
he talks non stop when he gets in the car with his brother who is 5yr. but once he get
into his school he just stops talking and he is not talking with his teacher or other kids.
he is been to this school for about 4 weeks and still he is not talking. i even changed his class to other teacher
still he keeps close mouthed in the school when i go to pick him up when no one is around he shouts and play in the school ground. i am really really worried please help me

[Kevin Kennedy, Ph.D.]

This condition is called selective mutism. While some recommend specialized intervention (viewing this as a variant of social anxiety), I think at this early point you should 'watch and wait'. This is a new situation for your son, and if all who are involved relax, act in a casual, matter-of-fact way (i.e., do not talk about the condition, do not put pressure him to speak), he will adapt.