Is it prealgebra or algebra? If it's prealgebra, I wouldn't worry too much because it's designed to fill in the gaps.
I agree with this, I almost think that at certain stages in Maths education nowadays they have a 'quality gate' class where the only intent is to ensure that there are no conceptual gaps or 'conceptual misalignments' and that all of the required foundational material is solidly in place before moving on to the next stage.
Any gaps from skips may show up at this stage and appropriate 'filling in actions' may be taken. Far from being bad, I think that a rigorous shaking of his knowledge designed to show and address any gaps (if any happen to exist) is a great thing because any gaps will only widen as he progresses. Examples of these 'take a breath and let everyone catch up' classes are pre-Algebra and pre-Calculus.
When I was a kid there was no such thing, you just 'rode the horse' until it threw you off or you rode it over the finish line. There was scant opportunity to climb back up into the saddle. One bad teacher was all it could take throw you off. I think the method these days is probably better for the majority of kids but can be painfully slow to gifted ones that are lucky enough to have good teachers.
