My concern is that he probably gets about 5 min. of instruction each day and then he's on his own. They are not doing any "curriculum" it is just random stuff.
This has always been a point of cencern for me - because "random" introduction of topics and working on them for a week or two would result in gaps in knowledge even though he is learning a lot at school time. This is one of the reasons that I prefer grade skipping to "differentiation".
When my DS was in an class where he got differentiation, he got no instruction at all - just worksheets. So, I taught him the concepts ahead of time using Singapore Math and Beast academy and also sent in a work packet from home. Will this approach work in your school setting?
Not sure. I think the problem that the current teacher is facing is huge gaps that he came in with in January. So he could do division word problems, but he didn't know how to measure with a paper clip. He must have missed the paper clip lesson last year in kindergarten when he fractured his skull.
She says she is "closing the gaps" but if it turns out he's fairly even now after the closing of the gaps, then I don't see why he couldn't do something like Singapore math, maybe a fourth grade level, with the teacher doing what she can to teach the concepts, maybe a little Khan Academy at school, and whatever I can do at home. I don't want to offend the current teacher though by saying that I don't think what is happening now is completely working (she has been trying so hard). We are actually putting him in a different district school so he and DD can be in the same school next year, so I am going to first meet with the current school, and then we will all meet with the new school so a plan is already in place before he starts.