I had my daughter (5th grader) retake it because she only qualified for the summer camp with her verbal scores and she wanted a science camp (needed qualifying math score).
We homeschool so she isn't used to these kinds of tests and I think it just hurt her the first time around. I spent some time with her discussing basics of taking tests (like keep an eye on the clock, make sure you answer every question and guess if you don't know). When she retested a couple of months after the first session she brought her scores up around 15 percentile points on each of those two sections and more than qualified for the science camp she wanted.
I realize this is not a popular opinion around here but I don't see the harm in making sure they understand the ground rules before they go in. Possibly he just had an off day? The other thing is he is getting compared against fifth graders whereas ITBS is usually against his own grade.
Consider repeating the testing.
