Employing achievement goal theory (Ames "Journal of Educational psychology," 84(3), 261-271, 1992), we explored science teachers' instruction and its relation to students' motivation for science learning and school culture. Based on the TARGETS framework (Patrick et al. "The Elementary School Journal," 102(1), 35-58, 2001) and using data from 95 teachers, we developed a self-report survey assessing science teachers' usage of practices that emphasize mastery goals. We then used this survey and hierarchical linear modeling (HLM) analyses to study the relations between 35 science teachers' mastery goals in each of the TARGETS dimensions, the decline in their grade-level 5-8 students' (N = 1.356) classroom and continuing motivation for science learning, and their schools' mastery goal structure. The findings suggest that adolescents' declining motivation for science learning results in part from a decreasing emphasis on mastery goals by schools and science teachers. Practices that relate to the nature of tasks and to student autonomy emerged as most strongly associated with adolescents' motivation and its decline with age.