My mother took a few courses at the University of Delaware when I was eight. I have one clear memory of it. She is sitting on the floor of our living room with books open around her, filling a spiral-bound notebook with writing. I don’t remember our conversation word for word. But I have always remembered the core of what she told me, which is that writing down what you are learning makes it stick. At the time, this made all the sense in the world to me. You can read something and remember some of it. But when you...