You can't use the grade equivalents for placement, but you certainly can ask that your child be placed with children with similar RIT scores, and you can use the RIT scores directly to find what level the child is performing at,
by using RIT curiculum ladders like the one here. .
And that is what I think they do at DS's school. They do a lot of ability grouping and it seems to be fairly automatic. I sent math homework back last year marked "He knows this already" with a few completed problems to demonstrate that he did know the material. Almost immediately he was tested and moved into a higher ability grouping. Or something. All I know is that the next week he came home bragging that he was in 4th grade math and he had appropriate level homework.
