Random factoid in response to your question: DS10 just took the SCAT for grade 5, compared to grade 8 norms. You have to be "in the 95th percentile" to write, but there's a long list of ways to qualify, including both achievement and cognitive testing. (It's a low bar and pretty easy to qualify, unlike, say, Davidson).
We received percentiles for math and verbal comparing him to both CTY's grade 5 "talent search group" and national grade 8 norms. His verbal score was middling, but 12 percentile lower compared to CTY grade 5s than national grade 8s. His math was high, but still 5 percentile less compared to the CTY grade 5s than the older kids.
You obviously can't extrapolate much from this, but I wouldn't be surprised if a typical group of out-of-level test takers could consistently outperform national norms set for several years older. DYS would be a whole different level. I also suspect this effect may be exacerbated when they are younger and aren't learning a great deal of new math from one year to the next.
Last edited by MichelleC; 03/19/15 04:50 AM.