To teach something (to someone) through repetition. A noun or pronoun can be used between "drill" and "in." The teacher tried drumming in the material before the state exams, but he was still concerned that the students weren't getting it. You never listen to what I'm telling you! Do I have to drum it in to you, or what?
See also: drum
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.