But you can tell a lot about a teacher by how they respond when students don’t succeed. Some will say, “What’s wrong with you?” Others will ask, “What’s wrong with me?” great teachers know three things: they know their subject, they know how to explain their subject, and they know their students. Knowing the history of a topic, the interesting problems, the common misconceptions, the multiple approaches, the links to other topics. And it’s about expert communication of all of that. They co-create educational experiences with their students because they realize that students hold key knowledge of their own that most don’t acknowledge or even recognize.

Paper wasn’t supposed to be cool. Then math came along.

The 1’s add no information. And so it’s more convenient to exclude 1 from the list of prime numbers. That’s what allows us to say that each number has a unique prime factorization.