In order to study physics one has to be ready to create and understand abstract concepts, to arrange them into structures. As demonstrated by Piaget through his teaching experiments, a child and juvenile pupil are not mature enough for this process. And this represents an essential obstacle in studying physics.
However, teaching is feasible even though the level of formal thinking has not been achieved yet. Namely, even if a student is not capable of proper formal reasoning outside the context, he can usually do it well enough in concrete situations. That is the reason why a propaedeutics course is quite possible. Moreover, it is really necessary. Thanks to it the student will be prepared for "proper learning". According to Wygotski [12], through such an approach he should even develop the skills of formal reasoning.