Relatively little empirical evidence exists concerning variations in the quantity of instruction across learning in complex, real-world tasks. Examination of driving instructors' remarks to pupils during actual lessons indicated the rate of comment declined in a coherent fashion across training, most consistent with a power function. The presence of a power law is reminiscent of learning functions found from studies in other skill domains when using indexes of performance, and suggests that quantity of instruction therefore might be used to assay the performance in complex tasks. The implications of these findings, for both basic and applied research, are discussed. Copyright © 2007 John Wiley & Sons, Ltd.