Research was performed in lower grade technical schools in the Netherlands to study complex psychomotor tasks requiring integration of several task-dependent skills. In two studies, students were observed performing metal work. They were assigned to instructional conditions of high, intermediate or low structure. Students in the high-structure condition had to perform the task according to a teacher-provided plan, which specified a list of actions students were required to follow. Students in the low-structure condition were given nothing but a design of the product, and they had to decide upon all necessary operations. On the average, high-ability students made better products in less time and used a relatively smaller part of that time for orienting activities than low-ability students. High-ability students performed worst under high-structure conditions, whereas low-ability students performed best under these conditions. A third study involved the performance of a wiring task. No instructions were given. Two strategies could be distinguished--a goal-directed strategy and a trial and error strategy. A tentative hypothesis involving a positive relation between spatial-technical ability and goal-directed strategy was derived. (LMC)