1. As has been already explained, when the teacher knows something about the instincts of children, he will utilize these tendencies in his teaching and work with them, not against them. He will, wherever possible, make use of the play instinct in his lessons, as for example, when he makes the multiplication drill a matter of climbing a stairway without stumbling or crossing a stream on stones without falling in. He will use the instinct of physical activity in having children learn number combinations by manipulating blocks, or square measure by actually measuring surfaces, or fractions by using scissors and strips of cardboard, or geographical features by modelling in sand and clay. He will use the imitative instinct in cultivating desirable personal habits, such as neatness, cleanliness, and order, and in modifying conduct through the inspiring presentation of history and literature. He will provide exercise for the instinct of curiosity by suggesting interesting problems in geography and nature study. 2. When the teacher understands the principle of eliminating undesirable tendencies by substitution, he will not regard as cardinal sins the pushing, pinching, and kicking in which boys give vent to their excess energy, but will set about directing this purposeless activity into more profitable channels. He will thus substitute another means of expression for the present undesirable means. He will, for instance, give opportunity for physical exercises, paper-folding and cutting, cardboard work, wood-work, drawing, colour work, modelling, etc., so far as possible in all school subjects. He will try to transform the boy who teases and bullies the smaller boys into a guardian and protector. He will try to utilize the boy's tendency to collect useless odds and ends by turning it into the systematic and purposeful collection of plants, insects, specimens of soils, specimens illustrating phases of manufactures, postage stamps, coins, etc. 3. When the teacher knows that the interests of pupils have much to do with determining their effort, he will endeavour to seize upon these interests when most active. He will thus be saved such blunders as teaching in December a literature lesson on _An Apple Orchard in the Spring_, or assigning a composition on "Tobogganing" in June, because he realizes that the interest in these topics is not then active. Each season, each month of the year, each festival and holiday has its own particular interests, which may be effectively utilized by the presentation of appropriate materials in literature, in composition, in nature study, and in history. A current event may be taken advantage of to teach an important lesson in history or civics. For instance, an election may be made the occasion of a lesson on voting by ballot, a miniature election being conducted for that purpose.