We used the Explore math results from ds�s 6th grade testing as supporting evidence for math subject acceleration when he switched to a different school after 6th grade. He ended up taking their (non-multiple choice, no calculator allowed) 8th grade placement test for confirmation. The Explore results, along with prior placement, grades and a letter of recommendation from his 6th grade math teacher, helped to convince them to allow him to take the above grade level test in the first place.
If your son�s gifted instructor is downplaying the Explore now, the results may not be important to your current school or district. Since your son is only nine, it could be insurance for some future negotiation.