Instructional systems development presents many problems for tasks that can be accomplished a variety of ways, and particularly for tasks containing unobservable processes. While unobservable processes are often ignored in instructional systems development, the way in which they are performed can have significant impact on operational performance. Evaluation of a tank gunnery trainer emphasized that considering only observable measures of performance when training gunners to engage moving targets was insufficient. The operational performance in hitting a moving target depends critically on the amount of lead applied. The correct amount of lead, in turn, depends on the target speed. There are, however, several different (unobservable) cognitive strategies for determining lead based on target speed. The current research demonstrates that the cognitive strategy selected for training will have a marked impact on operational performance, and that selection of a strategy to be trained rests on an understanding of underlying psychological processes.