Rationale: Theory is an important guide to practice. Teachers should know several theories of child and adolescent development and understand the influence of developmental characteristics on behavior. To be effective, a teacher must understand and acknowledge the uniqueness of each student and value their individuality, how they differ physically, cognitively, socially, and emotionally. A teacher must be able to identify the level of each student’s self-esteem and his or her need for psychological and social support.