While motivational changes towards science are common during adolescence, our work asks which perceived classroom experiences are most strongly related to these changes. Additionally, we examine which experiences are most strongly associated with learning classroom content. In particular, using self-reports from a sample of approximately 3000 middle school students, this study investigates the influence of perceived science classroom experiences, namely student engagement and perceived success, on motivational change (fascination, values, competency belief) and content knowledge. Controlling for demographic information, school effects, and initial levels of motivation and content knowledge, we find that dimensions of engagement (affect, behavioural/cognitive) and perceived success are differentially associated with changes in particular motivational constructs and learning. Affective engagement is positively associated with motivational outcomes and negatively associated with learning outcomes, behavioural--cognitive engagement is associated only with learning, and perceived success is related only to motivational outcomes. Theoretical and practical implications are discussed.