The aims of this study were to investigate the effects of discrepancies between teachers' perceptions of students' motivation and students' reports of their motivation on math and English grades and to identify possible gender and ethnic differences. Participants included 215 low-income, ethnic-minority students and their teachers in academically struggling schools. Discrepancy in motivation ratings accounted for a significant amount of variation in final grades. This teacher-student discrepancy effect was larger than both the effect of students' recent standardized test scores and the effect of self-efficacy in both subjects. Girls were found to attract positive teacher bias, but their grades were not differentially affected. Differences in teacher-student discrepancy effects between African American and Latino students were not found.