My DS was given the WJ achievement at age 6 and has developmental coordination disorder, is in therapy, and is on an IEP for being "physically impaired". He scored 97th percentile for math fluency for what it's worth. All of the "fluency" scores (incl reading fluency which also involves writing I believe) were his lowest scores. Same with my DD who has slow processing speed and writing issues.
DS's broad math score was 155 but the district refused to accelerate him even one grade for math. they claimed there are too many gaps. I did not see the WJ administered but have a feeling it doesn't measure the "standards" that kids are expected to know, like knowing how to identify something as a rhombus or quadrilateral. He scored around 96th or 98th percentile, for a national percentile, on the computerized math test (similar to MAP in that it tests above-level, but it was a different test). So there is obviously a difference in what the WJ is measuring and other tests of math achievement. His teacher has been working with him to close the gaps so it should be interesting to see how much his score goes up when he takes it again in a couple weeks.
I think his WJ broad reading score was pretty identical to what the computerized testing showed, around 97th percentile or 2-3 grade levels ahead. But for math there was a big difference. We were pretty much letting DS explore whatever math topics interested him rather than doing any sort of curriculum and so he was up to a fifth grade level for things like multiplication and division, but didn't know other basic things like how to measure with a ruler or use a protractor.
Don't know if this helps. Maybe aeh can weigh in on what the WJ is measuring and how it is different than other curriculum based measurements and if the WJ is really a good tool for figuring out whether a kid should accelerate and how much. Our district didn't care at all about DS's WJ test scores (even though they are the ones who gave the test to him as part of his IEP eval, so it's rather ironic).
