We had this very problem last year in k. I finally told the teacher that he was refusing to "read" the baby books. She then agreed to whatever I saw fit and let me send in books. He also had taken the Star test to get an AR level which put him 3-4 grade by November.
If she not not willing to help (as you've said you and your ds have tried), you need help from someone else- maybe the principal.
I'll be honest, even the principal didn't want to listen until we had outside testing results. My other comment is that experience with that teacher really hurt his self- esteem. It can be very detrimental to a young child to deal with, especially because they don't have the skills to deal with it.
Tell your ds you are working to help the situation. He needs to know you are trying. It's just a fine balance between support your child and not disrespecting the teacher (atleast in front of your dc).
Good luck! Keep us posted!
