This works for regular kids who improve with practice, but this is a kid with high scores who is thought to be able to do math several years ahead. So, repeating a skill until truly mastered is like writing your alphabet letters in 4th grade until they are perfect. Some kids will love it and comply and others will reach a "good enough" point from which they will deteriorate.
Kids who are more than regular gifted do not need as much practice. Over practice can get in the way of true learning. At least that's my experience with my kid.
Truly master a math concept is no easy job. For example, one seemingly simple question on median/average concept puzzled many top middle schoolers in recent AMC contest. Problem solving practice is not repeating, it is true learning for math. Actually it is the main reason that AoPS attracts so many gifted kids. For my experience, I never prepare any "repeating" worksheets, school homework is more than enough, instead, I'd follow the progress of hard problems DS came up with, encourage him discuss with his friends and teacher, to see how he could finally solve it.
