dajohnson60 wrote..."Does anyone know how IQ tests and achievement scores compare? My son's WJ-III achievement scores show 99th% or better on 10 subtests (>99.9 on 4). But when he was tested with the SBV his nonverbal was 98th% and verbal was 84th, giving him a full scale at 95%. The examiner did then use "select subtests" of the WPPSI for verbal skills as she didn't think the SBV captured his verbal skills. She didn't give numbers but said that he scored from above average to very superior on these subtests."
A term to know when understanding educational/psychological evaluation instruments is PREDICTIVE RELIABILITY.
Predictive reliability is the ability of on test/measurement/instrument to predict the performance of the individual on any other test/measurement/instrument.
Nutshelled that means any iq test has a PR that will tell you how reliable it is in predicting the child's performance on any other iq test or acheivement test. The same goes for the achievement test.
In addition, the PR will tell you how reliable that test is in predicting academic performance.
If the PR is low, then the test is pretty lousy and people aren't likely to use it. If it is high then its a pretty good indicator of abilities and performance and should match up well with other tests used.
Another thing to know is that from both achievement tests and iq tests you can extrapolate iq scores.
So if a child's composite score is 127 on the Wood**** Johnson III then it is very likely (PR is .92 to the WISC IV, I think) the child's iq would be within a half a standard deviation (+/- 7.5 pts) on the WISC IV.
Also, if you get a percentile score, you can extrapolate an iq score. If you are interested I'll find some websites with normal curve charts that will show you where a percentile rank falls on the standardized iq scale with 100 being the mean/average iq.
Standard scores can be extrapolated to iq scores (which are themselves standardized).
They are all just different ways of saying the same thing.
For your child's scores those difference are indicating failure at the ceilings of the tests used. The varied scores can also indicate learning disabilities and/or asynchrounous development.
