Have you tried looking for information about the test on either your school district website or the state education website? I'm not familiar with Arizona or the AIMS test, but fwiw there is a lot of detailed information about our state's standardized testing available online (including practice sample tests).
You might also call your school district's testing department rather than trying to go through your teacher, or ask a SPED staff member at your school.
One thing I'd also suggest doing - request a copy of your ds' full test report from your school district - in our district parents get a "report format" copy but there is more info available on some tests in student's big "file" that parents only get by requesting it. We had an issue with one of our ds' standardized school tests where he had a significantly lower score than expected, and it appears that what happened was he got off track using the test bubble sheet.
If you have other classwork and testing that shows a higher level of scores and work, I wouldn't worry too much about one test - any number of things can happen with any child on any given day. If, otoh, you've seen a pattern of lower than expected test scores or difficulty with classroom work in the area that's being tested and the low score came in, I'd be sure to follow up and get as much information about the test (were the questions read by the student, how did he have to respond, what specific skills were tested etc).
Best wishes,
polarbear
