What is the concrete noun of education?

There isn't one single perfect concrete noun for "education." Education is an abstract concept. However, depending on what aspect of education you want to highlight, you could use concrete nouns like:

* Textbook: Represents the physical materials used in education.

* Classroom: Represents the physical space where education takes place.

* Lesson: Represents a specific instance of teaching.

* Certificate: Represents a physical proof of educational achievement.

* School: Represents the institution where education happens.

The best choice depends on the context.