The educational importance of recognizing and dealing with differences between student and expert thinking goes well beyond the use of simulations. An apt metaphor is that of the student and the expert instructor separated by the mental equivalent of a canyon; the function of teach ing is to guide the student along the path that leads safely and effectively across the canyon to the nirvana of expertlike thinking. Guidance that ignores the student’s starting point or that is interpreted differently than intended usually just sends the student over a cliff. But education research, careful measurement, and new technology make it possible to guide most students safely along the path toward a true understanding and appreciation of physics.