What does your DS say about why he is not being cooperative? (I'd inquire about the math and the DRA separately.)
Just throwing this out there as a possibility - if he is aware that there is a desire on the part of one of his teachers to send him back down a grade, he may be reluctant to do anything that might show work that might be wrong for fear of being sent to the lower class in disgrace. He might not really grasp that not doing the work or cooperating with an assessment is practically guaranteed to get him sent back.
Feeling like he has to prove himself to stay in his class could be a big source of stress: most children may worry about getting bad marks, or even failing and being retained in grade, but they aren't worried about being sent back to a lower grade in the middle of the year.
I hope you can get this all straightened out soon in a way that works out well for you child. Hang in there.
