Jill, you will note that Willa Gayle and I had very different experiences with what the sub score discrepancies meant. In her child's case it was a sign of his learning disabilities whereas in my son's case it was an artifact caused by his being bored with the task. Both are real possiblities and it is obviously important to figure out which it is in your son's case.

You may find this helpful as you sort it out http://www.davidsongifted.org/db/Articles_id_10226.aspx
This article helped me realize that you need more than just a test score to get a diagnosis!