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The results are reported of a cross-sectional study of 4,084 Montreal schoolchildren between the ages of 6 and 17. Hand-wrist X-rays of the children were evaluated according to the Tanner-Whitehouse skeletal maturity system. When scored by the 20-bone TWII weights, the results revealed a slight delay for the French-Canadian children compared to the British standards. However, when measured on the separate RUS and carpals weighting systems, the French- Canadians showed a large advance by the RUS system but delay by the carpals. A reliability study was made of the bone-stage coding, which was converted into reliability estimates for the final scores. The observed differences of up to 50 maturity points on the 20-bone scores could just be due to inter-assessor bias in the coding, but the larger differences of up to 120 points on the separate systems could not be so explained. The opposing direction of these differences suggests that skeletal maturity cannot be treated as a unitary concept.