I think grade equivalent scales and mental ages are as important as z-scores. Suppose the distribution of intelligence were much more compressed than it actually is, so that only 1% of 10-year-olds were as smart as the average 11-year-old. You could still create IQ scores with mean 100 and standard deviation of 15, but the need to make special accommodations for children with IQ of 130 would not be so urgent, because they would not be that much smarter than the average child their age. When, in reality, 10yo children with IQ of 130 are about as smart as average 13-year-olds, this suggests the need for accommodations.
No. When a six year old ceilings out on a subtest, the result puts them at 16 yo equivalent (from memory, paperwork is in sleeping child's room). And that's just not correct.
That's because the WISC age norms only go up to 16 yo. Therefore the highest possible age equivalent cannot top 16-11.
Obtaining the same score as does not equal functioning at the same level as.
And to the previous point: 10 yo children with IQ 130 scored at the same level as the median 13 yo under the old mental age/quotient IQ. (Note that this is not the same as saying that they are "as smart as" average 13 yos.) No contemporary IQ tests use the quotient IQ, nor have they since the 1972 re-norming of the SBLM. Although efforts were made to scale deviation IQs so they would have some resemblance to the numbers generated by quotient IQs, they really are not the same measurement system.
Perhaps what would make more sense (though it's not as readily accessible even when the data exists) is to look at Rasch scalings, which figure item difficulty in. (This is the basis of the W score and associated RPI on the WJIII.) E.g., those with an RPI in a certain range are expected to be receiving instruction in their ZPD. Those below need remediation, and those above need challenge. Unfortunately, the RPI doesn't spread the upper end of the curve at all well, since it was designed for spreading the lower end.
