Zbigniew Michalewicz & Matthew Michalewicz 
Puzzle-based Learning [EPUB ebook] 
An introduction to critical thinking, mathematics, and problem solving

What is missing in most curricula – from elementary school all the way through to university education – is coursework focused on the development of problem-solving skills. Most students never learn how to think about solving problems.
Besides being a lot of fun, a puzzle-based learning approach also does a remarkable job of convincing students that (a) science is useful and interesting, (b) the basic courses they take are relevant, (c) mathematics is not that scary (no need to hate it!), and (d) it is worthwhile to stay in school, get a degree, and move into the real world which is loaded with interesting problems (problems perceived as real-world puzzles).