hi thank you for that. I have read conflicting advice which says do not offer your child rewards if ou think he is a selective mute. I am a primary school teacher myselfand have come across this condition myself. I am worried this is the case as he has told me outright that he will not talk at school.
It sounds like he needs to be screened then just to be sure. You can try taking him to the doctor and having him tested just to rule out any disorder. They can at least let you know if there is a reason to be concerned. Then if he is fine, try the reward system. It usually works for most kids.
Here is a resource to help you:
It certainly is a possibility that he might have this disorder. A screening should help you find out which issue he is dealing with.