In Common Core math, it often is not good enough to get the correct answer. Instead, students are required to show “higher order” thinking skills — in this case, use of the associative property. Yes, the associative property is important and should be taught at some point. Unfortunately, we suspect that many 7-year olds will not be able to understand this particular assignment.  With limited days in the school year, wouldn’t second graders — second graders! — be better off spending their time attempting to master the traditional subtraction algorithm?

https://twitter.com/sher2417/status/448281565609881600

Update:

In case you were wondering, the use of the term “friendly numbers” by the teacher above bears no relation to the use of the same term in number theory.