Good teaching/tutoring lasts throughout life. Not all teachers are interchangeable. A student I taught years ago recently said:
I passed my welding engineer course after three years of studying on my own and applying the basic principles you instilled in me.
I am now a certified Apprentice Welding Inspector recognized by the American Welding Society.
The skills you taught me allow me to outperform even on tests that are initially of an unfamiliar subject matter just due to the logic and the testing rules you taught me years ago.