8. To what degree may the activities of the school be made play? 9. Explain why the same activity may be play for one individual, work for another, and drudgery for a third. 10. Why should we seek to make the play element prominent in school activity? 11. When is one most efficient in individual pursuits--when his activity is play, when he works, or when he is a drudge? 12. Under what conditions should we compel children to work, or even to engage in an activity which may involve drudgery? 13. Explain how play may involve the maximum of utilization of the abilities possessed by the individual, rather than a type of activity easy of accomplishment. 14. In what does skill in the supervision of play consist? * * * * * X. THE SIGNIFICANCE OF INDIVIDUAL DIFFERENCES FOR THE TEACHER It has been indicated here and there throughout the previous chapters that, despite the fact that there are certain laws governing the various mental traits and processes, still there is variation in the working of those laws. It was pointed out that people differ in kind of memory or imagination in which they excel, in their ability to appreciate, in the speed with which they form habits, and so on. In other words, that boys and girls are not exact duplicates of each other, but that they always differ from each other. Now a knowledge of these differences, their amounts, interrelations, and causes are very necessary for the planning of a school system or for the planning of the education of a particular child. What we plan and how we plan educational undertakings must always be influenced by our opinion as to inborn traits, sex differences, specialization of mental traits, speed of development, the respective power of nature and of nurture. The various plans of promotion and grouping of children found in different cities are in operation because of certain beliefs concerning differences in general mental ability. Coeducation is urged or deplored largely on the ground of belief in the differing abilities of the sexes.