Words matter. They are principal vehicles of classroom instruction and lesson planning. The more clearly teachers articulate what is to be learned and the instructional practices to be used, the better they teach and the more likely students develop knowledge and skills. Words can be enigmatic. In education, many words have accumulated so many meanings that people interpret them differently. Sincere professionals might believe they are in agreement and engaged in complementary action for students’ benefit. But closer examination reveals that the specific actions they take vary so much that they rarely achieve shared goals. For example, there is evidence that a little struggle helps students better learn scientific or mathematical concepts and transfer them to new problems. In joint planning, teachers might agree on