For several years as a tutor, I always had this question, "Why does a student see a topic so difficult at school, whereas he manages to solve with ease in the tutorial sessions?"
The idea of the zone of proximal development unlocks the answer to this question. At school, the 'can-do' of students are less given consideration than in tutorial sessions. Of course, this is because of the ratio of teachers to students, limited time, etc. However, in a tutorial session, recognizing the zone of proximal development is the first step of the tutor. From there, the tutor guides the learner step by step and gradually challenges and promotes learning within the student. Later on, the student independently answers the problems and achieves mastery.
In my opinion, teachers have to extend their grasp of the students' 'can-do' in order to formulate accurate tasks for effective learning.