Consumes Activity Point?: YES
Choir Practice is an activity that allows all participants to earn Support points (affinity) towards each other. Byleth and students under him will also gain EXP for Faith and Authority Skills. If you practiced with students or Instructors who didn’t join you yet, they will not receive EXP for the aforementioned skills.
This is unlocked by completing the quest “A Passion For Music”, during the Hapstring Moon (05). To start this activity, talk to the Choir Coordinator inside the Cathedral.
Next, you’ll have to select two participants. The top selections (the ones with the blue arrows) are canonically good at music so they’ll benefit a lot with the activity. However, this doesn’t mean that you should only focus on them. You’re allowed to include any other character in the list but to maximize this activity’s benefits, have your characters that you want to train in Faith and Authority Skills participate, as well as those you want to gain Support points with.