The Gurukula System

Yathaa Khanan Khanitrena
Naro Varyadhigachchati |

Evam Gurugataa Vidyaam
Shushrooshuhu Adhigachchati ||

A man gets water (accumulated in the ground) by digging the earth with a spade.
Similarly knowledge in the Guru can be attained by serving the Guru.

This applies to the Gurukula system that existed centuries ago.The student had to serve the Guru staying at the Guru's place for years.The Guru would impart all the knowledge that he had.Not like some Profs of today who finally put their names on their students' patents/papers.
Also, today, education has become very expensive. Only people who can afford it can have it!!.