I'm sure she knows what's new, but if you're talking about 50 problems (or whatever) on a page, and five of them are on the new topic, and eight of them are on a topic he didn't ace the first time but maybe has mastered now (or maybe not), and another six are on a topic he did ace but it was a while ago and maybe he could use a refresher (or maybe not), and then seven are on something he's known all his life and can definitely skip, and three are on something he knows but now it's with bigger numbers (or combined with a different topic) so maybe it's a tiny bit challenging..... it's not all that easy for her to go through and say which parts he should skip. Even if he definitely knows the new material, unless he was in a position to test out of the whole year together, there could be something in that unit that he ~might~ need review on. It's just the way the curriculum is designed.
Among the homeschoolers I know IRL and online, I would say that Saxon is the most frequently dropped curriculum for kids who are mathy. It is extremely difficult to sort out what can and can't be skipped, and it's designed to repeat and repeat and repeat, adding challenge in tiny increments. For a kid who doesn't need that much repetition, and who can handle challenge in big increments, it really can just be a bad fit altogether. If you change what you want to change, between what you've said here and the fact practice in the other thread, what you're really talking about is dumping the curriculum entirely.
I'm not saying that's a bad idea, mind you... I have only very rarely heard of mathy kids doing well with Saxon, but you have to know when you approach the teacher that that's where this is probably headed. It's not a simple matter of tweaking -- you're really getting to the heart of the program and what it's designed to do.
