One area that ds9 and I and much of our extended family is weak in is "critical thinking". What IS critical thinking? Well, Wikipedia has a fairly comprehensible generalization of it. "Critical thinking clarifies goals, examines assumptions, discerns hidden values, evaluates evidence, accomplishes actions, and assesses conclusions." Basically, it is active thinking - as if interacting with the problem in one's mind. But more than that, it is the skill of actively deciding HOW to think - that is, deciding how to look at or approach a given problem.
There are countless examples of educational exercises which require critical thinking. Story problems, analogies, riddles, visual puzzles, code breaking, and so, so much more. And there are tons of workbooks out there with activities designed to help kids develop these thinking skills. But nearly all of these workbooks concentrates on just one area, such as thinking skills that relate to words and language, numbers and math, or geometry and visual perception skills. And very few workbooks have any exercises at all that challenge students with creative and abstract questions, requiring students to step back and actually decide how to think about the problem - which is the one area my ds9 needs the most help with. (And I know he's not alone in this!)
Evan-Moore's Critical and Creative Thinking Activities workbook is the exception to every workbook trend in this category. Not only does it have a HUGE variety of activities that exercise kids' critical thinking skills in every way imaginable, but it consistently goes about it in a way that requires kids to think outside the box a bit in order to come up with an answer. It's difficult to explain just how special and challenging these activities are - but if you sample the pages for yourself, I have no doubt you'll see what I mean. These are 3rd grade activities, and I find them challenging. Of course, that could be saying more about me than about the book... ;)
With kids like my ds9 who a little too bright for their own good and have a very black-and-white way of looking at the world around them, these types of activities are ESSENTIAL to help develop the part of their brain that is weakest, and can reap benefits to them across the board. There is no doubt in my mind that Evan-Moore's Critical and Creative Thinking Activities workbook is THE MOST VALUABLE WORKBOOK WE HAVE IN OUR HOMESCHOOL CURRICULUM. Needless to say, I highly recommend these workbooks. :)
Note that these workbooks are available for grades 1 through 6! Yay! You can sample these books almost in their entirety on Evan-Moore's website, but cheapest prices with free shipping are always to be had on Amazon or elsewhere.