Summary : Individual differences in arithmetic strategy use The present study examined individual differences in strategy use in the context of participants' use and execution of a heuristic for verifying mathematical equations, the five rule (i.e., reject equations that contain a 5 as a multiplicand and that have neither a 5 nor a 0 as the final digit of the proposed answer). The proportion of problems that violated this rule varied by block. Tendency to adopt the heuristic was inferred front the size of the latency and accuracy advantage for the five rule violations as compared with the false problems. Participants of varying skill levels differ in the speed and accuracy of executing the five-rule checking strategy as well as in the adaptivity oftheir strategy choices. Moreover, both low- and high-arithmetic skill participants used the five-rule on large problems only. The findings have a number of implications for understanding which variables affect strategy use and for understanding individual differences in strategy use. Key word : arithmetic, strategies, heuristics, individual differences.