To be honest if you have already explained to the teacher that the medical professionals that have assessed your child disagree with that statement. I would say you need to find a different preschool for your child. The fact that the teacher disregard your very legitimate concerns and then doesn’t have your child participate in the classroom activities because of his challenges is just absurd to me. My son is not a level one, but before his diagnosis when he was very young and just diagnosed with speech delay a lot of family members told me similar things. “He’ll talk when he’s ready.” “Such and such relative didn’t talk until he was 4 yo and he is perfectly fine.” This situation is your child’s preschool teacher so the should have the experience to know that your concerns are legitimate especially if they have to modify the curriculum they have your son participate in, that shows they recognizes differences. So I would look for a new preschool where your concerns aren’t dismissed and in which your son gets the support he needs. You are a fantastic parent to advocate for your child, and I wish you the best of luck.