Three Rs Meaning

(idiomatic) The basic precepts of any subject matter.

Example: The basic education received in primary schools. Literally; reading, writing and arithmetic.
The basic education any child can expect to receive, but not necessarily limited to reading, writing and arithmetic.
2002, Kids are Worth It!: Giving Your Child the Gift of Inner Discipline, by Barbara Coloroso
  Chapter 11: The Big C and the Three Rs: Chores, Relaxation, Recreation, and Rebellion