Can you tell me more about the issues you've seen with kids who have used Singapore's curriculum?
If the curriculum is used in whole (instead of in part) there is lots of review. Think about using the textbook, workbook, extra practice, intensive practice, AND challenging word problems books for each topic in each level! That much review would drive my kids batty. True, in Singapore they add timed computation drills (and most parents add even more practice at home). The teacher's manuals and home education manuals have extra practice AND drill listed for each topic.
I understand that people who don't use the curriculum as it is intended might have trouble. I wish we could get the message out that it isn't the curriculum's fault. (Many people fault Singapore's Primary Math and say it has little drill or review, etc., when in fact it is there if you choose to use it.)
I *do* like that it's easy to LEAVE OUT the extra practice books and therefore limit the review for kids who pick things up more quickly.
BTW My kids enjoy using the cd-rom games that match the curriculum. There's drill and extra practice in that.
