A thorough knowledge of the principles of adolescent psychology are important to administrative officers, county and farm agents and local leaders in dealing with the characteristics of boys and girls in the different stages of growth during the 4-H club age - from 9 to 21 years. This knowledge will enable them to understand their behavior characteristics of young people at different stages of development and to so plan the program that it will have an economical and social appeal at each period of their growth. The leaders also need to know the adolescent’s physical and mental possibilities and limitations at different stages of development. / M.S.