While motivational decline towards science is common during adolescence, this dissertation asks if there are beneficial science experiences that buffer against the loss of motivation and even promote its growth. The first paper examines whether classroom science experiences are differentially associated with motivational change and science content knowledge. Using self-reports from a sample of approximately 3,000 middle school students, this study investigates the influence of perceived science classroom experiences (student engagement & perceived success), on motivational change (fascination, values, competency belief) and content learning. Controlling for demographic information, school effects, and initial levels of motivation and content knowledge, we find that dimensions of engagement (affect, behavioral-cognitive) and perceived success are differentially associated with changes in particular motivational constructs and learning. The second paper examines one of these motivational outcomes (value) in more detail. Valuing science is associated with positive learning outcomes and is often used to motivate engagement in the sciences, but less is known about what influences its development and maintenance, particularly during the critical middle school years. Using multinomial regression applied to longitudinal data from approximately 2,600 middle-school students, we test the relationship of the perceived science experiences examined in Paper 1 (affective engagement, behavioral-cognitive engagement, & perceived success) and optional formal and optional informal experiences to changes in science utility value. Furthermore, we address whether the same factors that predict growth in science value also predict absence of decline. Overall, we find that all five factors are associated with changes in value, but some have different relationships with growth vs. decline outcomes. Together, these findings provide a more nuanced view of the factors associated with science motivation and learning (both in and out of the science classroom), as well as the practical implications for educational practice.