Most CCRS include things like trigonometry and symbolic manipulation of algebraic equations.
I see a lot of kids who can't do this.
Heck, I watched one kid years ago struggle with a question. "If a student spills acid on himself, what should he do. (a) Continue the experiment. (b) Tell a friend. (c) Tell the teacher when convenient. (d) Immediately rinse it off in water."
The student stared and stared and stared at the question. Finally the teacher in the classroom asked what he didn't understand. "Who spilled the acid on himself?" Without missing a beat, the teacher said, "Devante." "Well, then Devante had better rinse it off with water!" He was just that dependent on the detail; he couldn't generalize. If the quiz had said "If you spilled acid on yourself," that would have been fine. "A student" as a variable ranging over the set of all students was too much for him to process. Perhaps he had a disability, but if so it wasn't diagnosed.
Now put him in an algebra II class with symbolic manipulation, a physics class where Fnet = ma and he has derive Fnet for a block on a slope or a particle in a magnetic field. Hard enough to get kids like that to just be able to subtract two forces at 180 degree angles, while F = ma, m = F/a, and a = F/m are on the board.
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