3. As the problem series develops, there should be an increase in the difficulty of the problems. It is obvious that the simpler problems are to be used at the first of the series. To develop judgment to a desirable extent, the later choices will be determined from an increasing number of similar situations and from situations in which the degree of difference decreases as the problem series progresses. 4. Each problem series should involve as many types of life situations as possible. For example, applications of art are needed in the various phases of homemaking. (See Section III, pp. 18-21.) For that reason it is very desirable to select problems in each series from as many of these phases as possible. By this means the pupils are better able to cope with their own problems in which a fundamental art truth, or principle is the basis for adequate solution. The following detailed procedure is presented as an illustration of the way in which an art principle may be developed through a problem series. It may appear to be unnecessarily detailed and to require more time than the average teacher would have for planning. However, part of material here given consists of probable pupil replies and a description of the illustrative materials that are to be used. SUGGESTED PROCEDURE FOR DEVELOPING AN ABILITY TO USE A PRINCIPLE OF PROPORTION FOR ATTAINING BEAUTY An effort is here made to present the details of a teaching plan by which a principle of proportion may be developed by the pupils. This plan is spoken of as a lesson, but not in the sense that it is to be accomplished in a limited amount of time, such as one class period. The term _lesson_ is used to designate the _entire procedure_ from the introductory problem to the point where the pupils have developed the ability to use the principle of proportion. It will be possible to make more rapid progress with some classes than with others and in some class periods than in others. It is suggested that the teacher endeavor to evaluate the class time and plan so that the end of the period comes not as an interruption but as a challenge to further interest, observation, and efforts. The lesson suggested below should take not more than three of the short class periods of 40 to 45 minutes. If too much time is spent on one series there may be a lessening of interest because of seeming repetition. On the other hand, if sufficient applications and problems are not used after the principle is established, there is danger that the pupils will not be able to use it in solving other daily problems. Further suggestions for problems, illustrative materials, and assignments may be found on page 40. SUGGESTED PLAN FOR THE DEVELOPMENT OF AN UNDERSTANDING OF THE PRINCIPLE OF PROPORTION AND ITS USE _General objective._--To develop ability to--