Library books are arranged by the Dewey Decimal classification scheme whereby each subject is represented by a number. You will find books on the same subject will have the same number. The shelfmark is preceded by the letter D and will be followed by 3 letters, which are usually the first 3 letters of the author's name.
Useful education related subjects shelfmarks:
D 370 General education
D 371.1024 Classroom management
D 371.9 Special education
D 372 Primary education
D 373 Secondary education
D 378 Higher education