Changes and continuities in adolescents' optimal experiences over two years are explored in this study, and related to the development of affective and motivational patterns. Optimal experience, or flow, occurs when people do intrinsically rewarding activities in which they feel optimally challenged relative to their level of skills. The major questions addressed by this research concern whether increasing the frequency or intensity of flow is associated with positive changes in adolescents' cognitive and affective experiences both in and out of school. As participants in the Experience Sampling Method (ESM), 281 adolescents from 12 sites across the United States each provided an average of 32 reports of their daily experiences for one week while they were in the 6th, 8th, and 10th grades, and for another week 18 months later. Results expand on earlier findings by showing that those who increased in flow also increased in intrinsic motivation, self esteem, time spent doing school work, and in the relevance of their activities to their future career goals. Two tables and two figures present data and statistical analysis. Appendix A presents a facsimile of the self-report form (ESF) used by participants in this study. Appendix B defines the five variables of interest for this study. Contains 14 references. (Author/TS)