The moderating effects of motivation, social control, and self-regulation in predicting academic achievement were examined in Grades 11-12 for 3,281 seventh through nine graders. Standardized assessments of college readiness and student self-reported measures of psychosocial factors were used in the study. The results showed that females in Grades 7-9 scored higher than males for motivation and self-regulation. In predicting later achievement in Grades 11-12, motivation and social control moderated prior achievement, whereas self-regulation moderated both sex and prior achievement. Particularly among female students, effects of self-regulation were positive for high-achieving females (percentile rank [greater than or equal to]95) and negative for low-achieving females (percentile rank [less than or equal to]5) in predicting achievement in Grades 11-12. The phenomenon known as the "Matthew Effect" and implications for classroom teachers and educational policymakers are discussed.