"The Common Core math standards have been contentious since they were
launched several years ago, with many parents taking to social media to
complain about their kids getting incomprehensible homework. Kids are
now expected, for example, to explain how multiplication works using the
“box” and “lattice” methods. These methods take longer, and are harder
to master at first, but have been shown by some research to be more
effective than the multiply-and-carry method, particularly for kids who
have trouble memorizing things. And while they may be new for this
generation of parents, they have been around since at least the 13th century."
http://www.theatlantic.com/education/archive/2016/01/the-man-who-tried-to-kill-math-in-america/429231/