Your child was tested for a maximum of 10 minutes in that particular subject area, and he was stamped with the 17 from that experience.
I think this is the most important thing for parents to remember. These scores are not set in concrete and are not absolute. Just have your child tested several times and look at the results. Like Dottie, we're a family of multiple tests on multiplpe kids. One of my sons has had the WISC IV twice. One time he topped the VCI, one time he tanked it. Without the benefit of multiple tests on multiple days, I would never have had a clear picture of him. Not that any of the IQ tests really gave me that. After the benefit of a time (and the wisdom of advancing age!) I've learned to put very little stock in IQ tests anymore. There are too many variables in play - the test, the tester, the day, the location, the child's mood, etc. Get the test done to get into that school or program if needed, but then move on.