Setting aside for a moment that the article is concerned with K-8 specifically, college textbooks are just as horrible. Math (calculus) is the worst. TFA says that: "It could be that key information or steps are missing." If you wanted to teach yourself calculus, my calc book was the worst. Sure there would be some examples, but, in almost all cases, some term would magically turn out to be zero, one, or negative one, meaning that you got to skip a number of steps in solving the problem and never actually learned how to use the technique that was being taught. Fast forward to the problems for that chapter, and none of them are anything like the example.