my 6 years old refuse to communicate with his teacher

HI i am a mother of a 6 years old boy he is lovely but he has a very strong personality he's smart and chatty spoke 2 languages italian and english fluently.the problem is his behaviour at school .in class when the teacher ask him questions even the most simple he does not answer ..he look at her like she spoke chinese .at home he is able to read do its mats and other homework with no problem and not help but a school he act like "stupid" i told that to the teacher and she send another external teacher to evaluate my son .
Surprice my son not knowing that this woman was also a teacher he answer all the questions he was comunicating fantastically and he did not show any learning disability..but...my self and his teacher are really worry of is attitude as it is for the teacher hard to evaluate him should a bring him to a specialist?my son interact very well with all the other  children and he is very happy he like school and he like the teacher but i dont know how to stop this attitude of refusing to interact with the teachers please i need help thank you
please note that last year he was in another school than i moved house and he change school but this behaviour was exactly the same in the old school

[RockRose]

Sounds like selective mutism.

http://www.asha.org/public/speech/disorders/SelectiveMutism.htm

[tiredbuthappy]

more resources-
http://www.selectivemutism.org/
http://www.selectivemutismfoundation.org/