I don't know much about the Academy per se, and there are some on this board who know a lot, so they may chime in. I do believe, however, that it is for kids who are doing middle school level work, so unless your son is already working at that level, it might make sense to wait a few years.

You can take the Explore through your regional talent search, such as the Duke Talent Identification Program. There are other talent searches as well. When administered to younger students, it is considered an out of level test. It is normed for eighth graders, but talent searches administer it to 4th, 5th, and 6th graders. I believe that some talent searches will let a 3rd grader take it. The test is given in January and February only.

Here is a link to various talent searches, some of which offer the Explore:

http://www.davidsongifted.org/db/Articles_id_10260.aspx

The WISC must be administered by a licensed professional, usually a psychologist. You can look around for a qualified tester in your area, and you may want to look for someone who has experience working with gifted kids.

It isn't ethical to look at sample questions, although unscrupulous people may have posted them somewhere. The test is meant to be completely novel to the testee, and the materials themselves are supposed to be available only to licensed administrators. Exposing a child to sample questions before he or she took the test would render the results invalid.

If Davidson Academy doesn't work for your family right now, there is a lot of good information on this board about advocating with your current school to get a better fit and more challenge.