Updated research on this published on Substack:
Skipping Grades and Other Gifted Acceleration and
Real measures of intelligence"This graph comes from data from the Woodcock-Johnson IV Technical Manual, p. 279-280. (large pdf, link opens in new window.). Rasch measure Intelligence vs Age.pdf [Google Drive, single-page PDF (71kB)]" (See "Real measures of intelligence" link above for the live links)
This
spreadsheet allows you to figure out answers to placement, comparison and acceleration questions that were practically impossible before. One can convert among: adult IQ, child IQ, child percentile, W-score (absolute intelligence measure on the WJ-IV similar to CSS on SB5), future or past scores at different ages, and even find a child's percentile in a class of a different age, average IQ.
From the "Skipping Grades and Other Gifted Acceleration" post:
Children's adult IQ equivalents
Children's ratio (mental over chronological age) IQ equivalents
Grade Skip Tables - Maximum recommended acceleration for different class average percentiles: 15%, 30%, 50%, 67%, 80%, 90%, 95%; here's the one for an 80th- percentile average school or class:
College readiness - how does your child measure up against ideal academics?