Dazey,
Interesting questions. I really don't know the answers, but my impression from seeing sample problems of both types of tests is that the EXPLORE and SAT (and ACT) are more comprehensive in scope. They may also have quite different norming samples. For my purposes, percentiles calculated from the college-bound population are more useful.
It would be fascinating to know exactly what content is included on MAP. My guess is that the math does not go beyond Algebra I and basic geometry. In that sense I doubt that it actually has anything that you or I would think of as 12th grade material.
DD (4th grade) has done all three of the MAP tests now (2-5 survey math, 2-5 survey reading, and Language survey). Yes, the 2-5 math did not have much headroom. The Reading test, on the other hand looks like it has quite a bit of headroom in terms of content of the questions (and I have a highly verbal kid). The actual percentiles don't matter much as you can look up the same score at any grade level, so if your DS scores 99th percentile in math for his grade, then you can check the same RIT score in the column for 5th grade, 6th grade and so on.
Actually, it's partly because of those tables that I wonder about the test. There is far less change in percentile from year to year than I would expect to see.
For the language test the level doesn't matter since there is only the one level.
If you end up having your DS take the 6+ tests, please post more and share your thoughts. I had planned to use the MAP tests as a benchmark to check progress from year to year, but now I'm not so sure.
-NJMom
