I am posting this almost a year after this thread was started, but I wanted to make a couple of comments about the Duke TIP program. This thread came up on a Google search.
My son took the Explore test as a sixth grader. This test is normally given to eighth graders. In February he will take the ACT. He did quite well on the Explore test, but we found he had a problem with his reading score. This is something he can work on, and we were able to discover the problem because he took the test.
Students who do well on the ACT do get some educational opportunities that are worthwhile. Some are expensive, others are not. My son is already in algebra, and I think it's great that he will be able to take some practice tests and see what he needs to learn in math. The upcoming test gives him an incentive.
I think criticism of this program is way off base. Also, as has been posted, a child does not need to be "selected" by the school, although generally only kids in the gifted program are asked to participate. If your child has test scores in the 95th or higher percentile in any subtest on quite a number of different tests your child will qualify. So if your child has composite scores in the 90th or even 85th percentile range he is likely to have one subtest somewhere that is in the 95th percentile, and that one subtest qualifies. (The California Achievement Test, for example, has 10 subtests. The Iowa Test of Basic Skills has nine). So it is a very inclusive program.