Despite many assertions you may see, math knowledge can flow backwards and forwards, it isn't all a carefully stacked tower. Particularly true when you are looking at entering new branches like algebra or geometry, etc. If he is a self-motivated math learner, he'd back populate in any of the miniscule gaps.

With some chance that the instruction is slow, I'd suggest reading this article about Problems and Exercises and make sure the school isn't just supplying exercises: http://www.epsiloncamp.org/faq/faq_1.php

In a similar vein, it may be a good chance for him to connect with (if there are any) middle school teachers and students who are involved in math competitions.