Locke's great work, on which his fame securely rests, is the "Essay concerning Human Understanding," which stamps him as the greatest of English philosophers. This appeared in 1690. His most important educational work is entitled "Some Thoughts concerning Education." Compayré says, "From psychology to pedagogy the transition is easy, and Locke had to make no great effort to become an authority on education after having been an accomplished philosopher." Further, the same author says concerning the essential principles discussed in "Thoughts concerning Education," "These are: 1, in physical education, the hardening process; 2, in intellectual education, practical utility; 3, in moral education, the principle of honor, set up as a rule for the free self-government of man."
In Locke, for the first time, we find a careful set of rules as to the food, sleep, physical exercise, and clothing of children. While modern science rejects some of these, most of them are regarded as sound in practice. Plenty of outdoor exercise, clothing loose and not too warm, plain food with but little meat or sugar, proper hours of sleep, and beds not too soft, early retiring and rising, and cold baths, are means prescribed to harden the body and prepare it to resist the attacks of disease. "_A sound mind in a sound body_" is the celebrated aphorism which sums up Locke's educational theory.
As to moral education, Locke declares, "That which a gentleman ought to desire for his son, besides the fortune which he leaves him, is, 1, virtue; 2, prudence; 3, good manners; 4, instruction." In his course of study the idea of utility prevails. After reading, writing, drawing, geography, and the mother tongue are mastered, Locke, like Montaigne, would teach the language of nearest neighbors, and then Latin. Even the Latin tongue should be learned through use, rather than by rules of grammar and by memorizing the works of classic authors.
While his system of education was planned for sons of gentlemen, Locke urged the establishment of "working schools" for children of the laboring classes. This was in line with his utilitarian ideas, as the intent was not so much intellectual training, as the formation of steady habits and the preparation for success in industrial pursuits. Locke's plan was for a sort of manual training school, the first appearance of such a project in history.