My son just finished - Kumon Reading - Grade 6.
This one was pretty good. As one might expect, it's simply short reading passages and follow-up questions. There's a whole lot of good, challenging vocab in there as well.
Luckily, my son doesn't complain about doing these, ever. I try to make him do 2 pages a day, sometimes 4. A 74 page book, these Reading books are good for a month or so. In fact when he got near the end yesterday, he asserted that I had promised him a *prize* when he finished it. I probably did but couldn't remember. Egged on by material greed, he took the book outside and finished off the last 10 pages on the deck all on his own. It's amazing what kids/people will do when sufficiently and basely self-motivated!
The Prince is also chugging along with his algebra. Check out his latest blog post - Imaginary Numbers.
And to see the mountain of workbooks he did before he was even 5 - click here.