high-ability students spend their time pushing through activities that don't just let them demonstrate mastery; they can get caught up on weird language and rules that aren't really necessary if you already know what you're doing
Everything else we've ever struggled over has been terminology, weird gimmicks, and lengthy ways of doing things that she instinctively knew how to do another, simpler way.
Oh, god, the vocabulary. DD8 was placed in 4th grade math this year mostly because she didn't know the vocabulary. I have no problem with teaching the "associative principle" and the order of operations, but are you seriously going to tell me that my daughter is not ready for a higher level of math because she doesn't know what a "minuend" is?
