In this two-wave longitudinal study, concurrent and longitudinal relations among teacher-reported shyness, peer acceptance, and academic achievement were examined (Ns = 162 and 155; and Msage = 6.09 and 7.07 years). Concurrently, at both times, shyness was negatively related to peer acceptance and academic achievement, and peer acceptance was positively related to academic achievement. Longitudinally, shyness was negatively related to peer acceptance, and peer acceptance was positively related to academic achievement in zero-order correlations, but the relations were no longer significant when accounting for the stability of the constructs. Longitudinal relation between shyness and academic achievement was nonsignificant; however, shyness was indirectly linked to concurrent and later academic achievement through peer acceptance according to bias-corrected bootstrapped confidence intervals. Sex differences in the relations were mixed. These results suggested that a lack of peer acceptance may be a mechanism through which shyness contributed to poor academic achievement in the early school years.