3 year old exhibits selective mutism

I was wondering if anyone else has had experience with this. In short, our son, in the absence of one of his parents, will literally not speak. This happens at school and with babysitters.He goes to an assisted pre-k every morning of the week and has failed both a hearing and sight test because of his refusal to say a single word. Last week one of his teachers called because for the first time he'd shown (through pointing) an understanding of colors. I've had multiple conversations with his teachers that they simply don't know what he knows. They say he's happy, smiles a lot, appears to enjoy being there ... he just doesn't talk. He's been going since the beginning of the school year.Before turning 3 he was in a program that supplied speech, developmental, and occupational therapy.He is not shy. He will strike up a conversation on the street with total stranger. He will ride ahead of his sister and me on his bike to the park and try to get other kids will ride their bike or scooters with him.The thing is, when I go with him to school or walk him out to the bus, I've seen a "switch" happen from the talker to the non-talker.Anyone have this kind of experience? via /r/Parenting http://ift.tt/2FOPS7W