Gave these out as end-of-the year rememberances to the 4th and 5th graders at an elementary school Math Pentathlon club. Next year, if I can find a sponsor, I plan to hand them out as the beginning of the year as de facto textbooks for that age. Used it over the year to teach how to do math in their heads to make them faster at the games. Usually took 10-15 minutes at beginning of club meeting to work on mental tricks, mostly from this book (or Khan Academy), and an hour and a quarter practicing the five games which are part of the Math Pentathlon competition.  In one school year with once per week after-school practice, my group wasn't able to get too deep into the weeds. But the instruction piece really helped their level of competitiveness on the games, especially learning to add and multiply (relatively) large numbers in their heads. The trick about multiplying by eleven alone will delight even a struggling math-o-phobe.<br><br>Some parts are well-written, some a little dense and repetitive. Getting good at these tricks really does require practice (along with already knowing one's multiplication tables). But if parents are putting time in at home to practice them with their kids, the payoff would happen pretty quick. Very useful techniques, once mastered.<br><br>Just reading this book won't make you better at math. But reading it and doing all the practice activities will. You'll get out of this book what you put into it.