Hi and welcome! It doesn't look like the teacher understands your DS, or maybe doesn't want to. I agree that summer school is not a good idea - making him cover material that he already knows will be no help! It is good to know that your ped. is helpful and that she can see how ridiculous the situation is. Unfortunately I don't have much advice to offer other than looking at other schools (if this is a possibility?) or homeschooling. Is there anyone in the school that you can talk to? Do you know who your DS's teacher will be next year and how they feel about things? You are in a tough situation, but at least you have found this board - there is lots of advice here.
I also just want to add that my DS4.5 will often say that he "doesn't know" just to avoid any possibility of getting things wrong. He also spoke late, but when he started he spoke in sentences - it was like he didn't want to try it until he knew that he could do it. Maybe your DS isn't feeling secure enough in class to try and answer questions?
Sorry I can't be more help, hopefully others will have something else to add.
