My dd also took the Explore test this past year. In learning about it here on the forum it was explained to me that the Science section is much more a critical reasoning test than a Science knowledge test.
Depending on how well the principal, etc, know the Explore, this might not be enough ammunition to get him accelerated in Science. Is there a way to "prove" that he knows the concepts in the textbooks? For example, in math, you can test out of classes...