Education without this is like building a sandcastle. The brain is going to discard the information after the test if you aren't required to reexplain it the next year, and your foundations get eroded.
This "discarding after test" is already and automatically addressed in the education: high school repeats things learned in previous schools and builds on those. Our high schools also have large final exams that require one to be able to understand the whole curriculum of the subject. The grade measures your memory, and understanding because you cannot just memorise everything. The same is true for all education levels.
Under the principal of spaced repetition, you might also want people in the workforce infrequently tutoring college students, graduate students infrequently tutoring high school students, college students infrequently tutoring middle schoolers, so on and so forth.
The teacher-student heirarchy was decent way to mass produce educational services during industrialization but creates unnecessarily rigid classifications between learners at different levels of knowledge.
I think there is room for a more mutualistic exchange, between tutors who would like to clarify their existing knowledge, and between students who like to learn something new, to emerge in the future.
We are also having university "students" tutor younger people. These are called teachers and professors.
k-12 (13 yrs), Collage (4yrs), Med School(4 years), Residency (3 years), Specialty medical training (3yrs) = 28 years. Ignoring pre k and the fact that this is the happy path.
Residency starts out with extreme levels of supervision. The end of fellowship is the point where they are considered competent enough to not need direct supervision. Though doctors still have plenty of people looking over there shoulders.
The point is 32 is when doctors can start paying back significant amounts of there student loans and saving for retirement. Including interest it's not hard to be 32 and have 1/2 million in debt.
PS: Also, specialist's can't afford to make the path cheaper for the next person as they need to constrain supply to keep there wages high. Which not only increases cost of healthcare, but also medical research.