Achievement goal theory distinguishes between mastery goals (the goals of developing competence) and performance goals (the goals of demonstrating competence) [Ames [1992] "Journal of Educational Psychology" 84: 261-271]. In this study, we employed this theory aiming to better understand why adolescents' motivation to learn science declines with age in many schools yet not in others. We collected survey data from 5th to 8th grade Israeli students (N?=?1,614). Utilizing Structural Equation Modeling (SEM) methods, we investigated the relations between students' perceptions of goals emphases in their environment (by parents, peers, teachers, and schools), their own goals orientations and their engagement in science learning in and out of school (classroom and extra-curricular engagement). In addition, we compared between these relations in traditional and democratic schools and in elementary and middle school grade levels. Findings show that: (A) perceptions of the goals that significant adults (parents and teachers) emphasize were better predictors of students' motivation, in and out of school, than perceptions of the goals that peers and schools emphasize; (B) perceptions of teachers' performance goals emphases negatively predicted classroom engagement; (C) the relative effect of perceived parents' mastery emphasis on extra-curricular engagement was higher in elementary grades than in middle school grades; (D) the relative effect of perceived school's mastery emphasis was higher in middle school grades than in elementary grades; and (E) students' mastery goals orientation in science class was a strong predictor of their extra-curricular engagement. Implications for both research and practice are discussed.