We have used the Standards (homeschooling) and Math in Focus (public online school). Singapore math in general seems quite a bit more advanced compared to typical math programs in public schools. I really like the Singapore approach to math, but it worked much better for us in a homeschool setting because there are areas that advanced kids might need to skip, or go through really quickly, and public school isn't really set up to accommodate that. I think there is a generalized opinion (in schools) that it is rigorous math, so it should be good enough for advanced kids.
There is a computer component called Math Buddies, that goes along with Singapore Math, I would see if the school is offering that because that might be a way to differentiate for at least part of the class time. I also agree with Kai that the workbooks Challenging Word Problem offers more advanced problems, but in our experience they will still be too easy if your child is working much above grade level.
