In the mid-1970s, Ference Marton and Roger Säljö of the University of Gothenburg in Sweden noticed that their students took different approaches to learning. Some focused on remembering information, others on understanding it: connecting it to other information, figuring out when it might be useful, and so on. Marton and Säljö christened the former surface learning and the latter deep learning.

In 1924, Sidney Pressey, a professor from Ohio State University, invented a teaching machine. The mechanical device, about the size of a portable typewriter, allowed students to press one of four keys to answer questions curated by expert instructors. A later version dispensed candy for correct answers. Education optimists were fascinated, and Pressey promised the technology would accelerate student learning. But the machine was a commercial flop.