We investigated (a) the associations of implicit theories and epistemological beliefs and their effects on the academic motivation and achievement of students in Grade 6 science and (b) the mean differences of implicit theories, epistemological beliefs, and academic motivation and achievement as a function of gender and race/ethnicity (N = 508). Path analysis revealed that an incremental view of ability had direct and indirect effects on adaptive motivational factors, whereas fixed entity views had direct and indirect effects on maladaptive factors. Epistemological beliefs mediated the influence of implicit theories of ability on achievement goal orientations, self-efficacy, and science achievement. Results are discussed in relation to Dweck and Leggett‟s (1988) social-cognitive theory with a focus on middle school science.