The model was derived from a longitudinal study of young adolescents followed over a seven-year period, and focuses on the transitions in and out of adolescence. Three aspects of the life-course perspective are relevant to the model: the concept of the entire span of life, the role of social contexts in individual development, and the influence of normative expectations for the timing and sequence of developmental changes. Normative life events, including school, marriage, birth of a first child, and retirement, involve new expectations for the individual; this model adds the concepts of process and differentiation in developmental patterns. The challenges of new expectations may be experienced by the individual in a growth-enhancing way depending on his strengths and vulnerabilities, the extent of the challenge, and the available social support. Problem behavior during adolescence, defined as that which defies age and sex related norms, is the result of inadequate coping with these developmental transitions. In some cases, adaptive behavior which may fulfill immediate developmental goals ultimately leads to diminished developmental competence. This model was tested with a sample of upper-middle class adolescents with basically good resources available; 55 percent were characterized as having stable good functioning, about 11 percent stable poor functioning, and the rest variable. Over the adolescent decade, declining functioning is more likely than improving functioning. Prevention and intervention in terms of preventing poor self-esteem, alcohol and drug abuse, and school disengagement, would be most effective during these transitional periods. 5 figures, 49 references.