This study examines the convergent validity of the Physical Activity Questionnaire for Children (PAQ-C) for assessing moderate-to-vigorous and total physical activity (PA) in school children. 430 participants (51.6% girls) aged 9-12 years provided valid accelerometer data (wGT3X-BT) and completed the PAQ-C. Convergent validity was assessed using Pearson correlations (r) and Bland-Altman plots. The PAQ-C total score was similarly associated with moderate-to-vigorous PA and total PA (r = 0.28 and 0.26, p < 0.001, respectively). 10- and 11-year-old groups were the only in which the PAQ-C was significantly associated with both accelerometer variables (p < 0.001). Girls showed higher associations (r = 0.31 for each, p < 0.001) than boys (r = 0.18 and 0.15 for moderate-to-vigorous PA and total PA, respectively, p < 0.05). Acceptable measurement bias for all age groups (range, 3.6-7%) was found. Researchers should be cautious when using the PAQ-C to assess moderate-to-vigorous PA in school children.