The objective was to develop and validate a patient-based grading scale for PedMIDAS. PedMIDAS was administered to 329 children, who rated their overall disability based on the adult MIDAS grades. This patient-based rating and PedMIDAS scores were compared to develop the grading scale. Headache disability was rated little to none, 49.5%; mild, 26.7%; moderate, 15.8%; and severe, 7.9%, with PedMIDAS raw scores of 4.9 ± 6.3, 17.8 ± 14.9, 40.6 ± 34.2, and 91.4 ± 69.8. Convergence of these results yielded an empirically derived grading system: Grade I, 0–10; II, 11–30; III, 31–50 and IV, > 50. Higher grades corresponded to an increased need for prophylactic treatment. A patient-based grading scale further increases the utility of PedMIDAS in assessing migraine disability in children, so that it can be widely used in routine clinical evaluation and management.