Can I offer a different approach? There is so much that’s mathematics out there that’s not covered in elementary school, and this stuff is fun, and better yet, it doesn’t make the match between your child and school even worse.
Problem solving, logical thinking, and abstract or algebraic thinking are within reach for many gifted kids in early elementary school. Why not extend and enrich in this manner instead of the death march of arithmetic?
We aren’t workbook people, but my kids have enjoyed Grid Perplexors and Balance Math, particularly for car trips, plane rides and waiting rooms. I have a smattering of a few ipad/ipod games that don’t look like math at all, including DragonBox, KickBox, BigSeed, Fractile Plus, TinkerBox, Rails and Trains. But most, we play games, chess, checkers, Mastermind, Parcheesi, Settlers of Catan, Forbidden Island, Pandemic, Ticket to Ride, 24 (ok, this one looks like math), Set, Blokus, Mindtrap, Khet, Yahtzee (also thinly disguised, but also teaches probabilities), and many, many more.
In the spirit of asynchronies, we’ve become adept at modifying almost all games to level the playing field between parents and siblings.
We also read, including Theoni Pappas' Penrose the Mathematical Cat and Math for Kids and Other People Too, Hans Enzenberger's The Number Devil, and Tahan's The Man Who Counted. More in line with the math that’s taught in school are the Sir Cumference series of books.
When my kids are up for much more passive consumption of math, they find good stuff on youtube, including Vi Hart videos and how-to origami folding.
Any other suggestions? We're a game family, so we're always looking for more ideas