1.The main principle is that students have to be challenged, the learning should not be too easy or not too difficult. The difficulty is mainly determined by the necessary degree of independence of the students and the complexity of the assignment.
2.The degree of independence of the students can change from (1) teachers-centred, (2) both teacher and students decide on the learning activities and (3) student-centred. The independence of the students should increase during the program. The amount of independence is reflected in the learning objectives, the cases or problems, the degree of self-study and the sources of information.
3.The complexity of learning tasks range from simple, through average to complex. It is reflected in the aspects: a.the clearness and the amount of not relevant information in the case or problem, b.the necessary time available and/or necessary to finish the assignment, c.The level of the necessary entry knowledge and skills and d.the number of involved disciplines involved in finding the right solution.
From an internal document LUMC and ICLON Leiden University (Dutch) from Vink and Vermunt.