Simple elements of mathematical proof were analyzed by considering the making of a proof as a complex problem-solving task. Quantitative measures of performance on certain problem-solving tasks were obtained in order to determine the relation between problem-solving ability and chronological age (6-18). A consideration of all variables suggested that, even though problem-solving ability does increase with age, certain aspects of problem solving that approximate mathematical proof can be dealt with successfully in the upper elementary grades. An analysis of problem-solving strategies is recommended as a further step in the investigation of problem solving. IQ, reading ability, and mathematical aptitude are suggested as possible covariates or blocking variables in future research.