Sorry! Late to the party! :-)
As a PP said, the 2-5 test is a different "style" of test than the one your son probably took last year as a 1st grader. We used to have 1st graders take the 2-5 test in the spring as a qualifier for our high ability program (they had already tested high on the 1st grade MAP that spring in order to get into the testing pool) and there was frequently a definite discrepancy between kids' scores on the 1st grade test and the 2-5 test (though they were taken just a couple of weeks apart).
I think it will be fine and you'll see some pretty dramatic "growth" this year for him on that test. If nothing else, his teacher is probably thrilled because he/she will end up looking like the genius when your son grows about 30 points this year. ;-)
