DD is at a gifted magnet that does this as a matter of course. It seems to work pretty well as far as I can tell. They use two math books in a year. However, this is done for the entire class, so it's not like she's going it alone. I'm not quite sure how they manage without skipping stuff. I think they pretest, so maybe they do skip sections that everyone is strong in. I do notice that they have not gone in order at all.