If Topic X is a prerequisite for Topic Y, then you should cover Topic X before Topic Y.
If Topic Y is a prerequisite for Topic X, then you should cover Topic Y before Topic X.
If neither topic is a prerequisite for the other then you may do the topics in either order, or do them at the same time.
But how much proficiency should be required in Topic X before moving to Topic Y? Understanding of the topic? Being able to do the arithmetic without using fingers/calculator?
On the subject of mastering arithmetic, , I waiting until DD completes her pre algebra class before I let her have a calculator because the AoPS class really emphasizes mastery of how to solve the problem first, I.e, get optimal algorithm for tackling the problem decided first
before actually tackling the routine exercise of performing the calculations that I feel that if she demonstrates competence here that the mastery of arithmetic will thus be implicitly present.
