Medical students were provided with behavioural objectives for the problem solving phase of their curriculum. They were assigned for 11 weeks to various hospital settings that differed in the presence or absence of structured classes, the expertise of the teaching staff, the amount of instruction time and the types of learning experiences. At the end of that time, the students took the same examination to measure attainment of the objectives. The only variable that was associated with significantly different examination scores was presence or absence of structured classes.