It's very important to tell your son that a MAP test is 'opposite day' where the smartest kids finish last. Depending on how old your son is, you might want to ask him how he would build an AI that tested achievement. See if his answer reveals that kids who know more have more questions asked of them - the point of the MAP test is that if you answer correctly, the machine will give you more and more harder questions until you answer incorrectly.
Sometimes teachers mistakenly tell kids to 'just push the 'I don't know' button' to get it over with. I think I'd warn my kid not to do that.
MAP is an overall very good test. It gets in trouble with kids who make intuitive leaps and are able to answer some of the 'harder' questions but not all of them, perhaps only because they haven't been exposed to the notation being used, but the understand enough of the concept to be able to 'guess' using logic.
I hope this helps!
Grintiy
