We started our 11 year old son on the 5th grade Kumon books back in the summer, so that he wouldn't lose any of his previous years' knowledge. He blew right through every one available for 5th grade, and we're now onto the 6th grade level. We have had a rule of 30 minutes a day in the book- on top of any homework he has, and doing this has enabled him to go from a "B" student in math, to being an "A" student in the advanced math class! We're hoping that he will be able to get through the remaining 6h grade books before he finishes his 5th grade year, so that by summer he will be onto the 7th grade books, to stay ahead.
He does not get bored with the way the books are set up, which is a huge plus in comparison to some others we have tried over the years.
We couldn't be happier.