Maybe too late for your purposes, but I just saw this post. DS took the test in 7th Grade and qualified to do all the summer classes. I'm not going to lie; the courses are expensive. However, it gave DS a chance to try different academic areas surrounded by a bunch of pretty smart kids while visiting different college campuses. He made many friends that he stays in touch with. He did bio/chem, mock trial, Econ, and EE courses, which helped him to figure out what he might want to study in college. Right now he's a senior, Sea Cadet Petty Officer, and has applications in to a bunch of Engineering schools. He wants USNA (plan A) and USMA (plan A(1)). He's already admitted to a university that he likes with ROTC/NROTC, so plan B is in good shape. I'd say that DukeTIP was a big help in getting him to where he is today.
I know others who took the test, and didn't make the cut for the summer programs. Their parents tell me that it was a good experience anyhow, because the kids know what taking the SAT is like, and they are motivated to perform better later. YMMV. Good luck!