DS (5th grader) never took the tests, but his friends on AoPS told him that SAT/ACT math was extremely easy compared to the middle school math competitions such as CML, AMC8, AMC10, and mathcounts. While DS took those contests in the last two years, so he is not afraid of "hard" tests. Last week, he challenge himself with the ACT online test without any prep and no knowledge of geometry and trig (he is in an Algebra 1 class).
He scored Math+Reading+English+Science = 35+29+24+24. Composite score was 28. His math score was converted to SAT 780 with only two careless mistakes.
I never took the ACT, only the SAT. In the old days, I was told that ACT was move "achievement" oriented whereas SAT was more "ability" oriented. I was never exactly sure what that meant. Now that you mention it, the ACT would be a better way to track DS' progress since it is in the same format as the Explore so you can easily see the "growth". I was/am leaning towards the SAT only because SET only accpets the SAT and because that is the only test with which I am familiar. Are you planning on having your DS take the actual ACT at some point?
