Two studies were conducted to determine how students perform psychomotor tasks and how teacher behavior influences performance. Study 1, conducted with about 100 technical students in a metal working class in a technical school in The Netherlands, showed that a process-based heuristic approach, stimulating students to perform complex psychomotor tasks in their own way, can help both high and low ability students. Heuristic instructions permit students not having problems to proceed quickly through the successive processes that lead to the product. However, for students who encounter a problem, suggestions as to the means to deal with it are available. At any stage students themselves control each step of task performance, thereby strengthening their self-regulation capacities. Study 2, conducted with 18 teachers, 10 metal work teachers, and 8 electrotechnics teachers, recorded their verbal behavior during regular practice lessons lasting about 1.5 hours each. The study showed that technical school teachers are inclined to exercise extensive control over student performance. Taking into account the results of study 1 and of earlier studies, such teacher control should be regarded as ineffective: high ability students' performance will be lessened, while for low ability students only short-term effects are expected. Control over task performance should, therefore, be shifted from teacher to student. Teachers' instructions will be more effective when they put students in a position where they can invent solutions for problems and develop performance routines themselves. Special emphasis should also be put on the process of goal-image formation. (KC)