I'm looking at them as an measure of what he's being taught in the classroom. My understanding of the instrument itself is that the scores are tied to material covered relative to educational standards.

So, a math score of 190 should reflect a general skill level across multiple mathematical skills - operations, number sense, algebraic thinking, etc. If the student is being introduced to new material and improves in old material, their score should increase (vven if their percentile doesn't change). If they're not being introduced to new material then their scores should stay relatively constant. Whatever the new score, it will reflect general skills again.

I don't think that's a reflection of if the child is being adequately challenged but more of a reflection of if they're being exposed to new material.

I don't know what to say about your how your sons' schools use them or even how other schools use them, I've read a variety of different things. Some talent searches look at them, some gifted programs do as well. I've read a decent number of threads on here about it as well. I agree that they're not a panacea but I wouldn't put them in the category of worthless either.