When programming a piece, the question to ask is: How will this challenge them?
Every piece you program will offer challenges. Those challenges will be addressable in rehearsal after you’ve encountered them. But if you can anticipate the challenges, then you can more effectively teach from the beginning to ensure that the challenges are surmountable.
This will challenge their ears. This will challenge their memory. This will challenge their vowel production, their tone, their musicianship. This will challenge their reading skills. This will challenge their poetic understanding.
As often as not, I’m surprised at what the challenge is when I teach a piece for the first time. Even so, I am always trying to anticipate before I start.