At a clinic sponsored by a prominent piano pedagogy publisher, the clinician asked a very interesting question. "Why are you teaching your students? What is your purpose, and what is their purpose?"

This is something we need to ask ourselves on a consistent basis. He continued to point out that almost everyone we are teaching will not make it to Carnegie Hall or even have a profession in the music field. That being the facts, make sure what you are teaching is enjoyable and fun, and that your students will not only have a life-long appreciation for music, but find pleasure in simply playing for themselves.

With various literature available this can easily be accomplished. Teach them the basics in theory, technique and standard classic literature. Supplement with "fun" music they might hear on the radio or pieces their friends and family might recognize. Even these pop pieces can be dissected to illustrate what they might be currently learning in their core method books.
This is what will keep your students playing while providing a meaningful experience, rather than leaving them frustrated, disillusioned and perhaps never playing another note for the rest of their lives.