The pedagogical discoveries involved have required genius, but the teachers who are to apply them do not require genius. They require only the right sort of training, together with a degree of sympathy and patience which is by no means unusual. The fundamental idea is simple: that the right discipline consists, not in external compulsion, but in habits of mind which lead spontaneously to desirable rather than undesirable activities.
Source: On Education, especially in early childhood, 1926, chap. 1:Postulates of modern educational theory.