This is a version of the band lesson I use.
I will do this slightly differently in my Senior choir class (which is 1-1) and my Freshman choir class (which is 1-2). I will do this as a "station" in freshman class while the remainder complete SmartMusic sight-reading assessments.
Senior choir has some prior knowledge of key, chords, measures, etc... Freshman choir has little of that.
I model opening Garageband and recording a drum track, bass track, and keyboard track. I use Smart instrument settings and autoplay. I show them how to check that the chords are available for a I-vi-IV-V sequence. I stress we will use only these chords. Garageband defaults to an 8 measure composition. I spend maybe five minutes on this demonstration.
I ask them to compose a five track composition with a melody on top of them singing. There must be two vocal tracks. They can do it in monophonic style or polyphonic style (we are singing motets at the moment). This opens the assignment up to lots of discussion about choices. I give them 30 minutes.
One thing I will do with the choir is insist that they do the tracks in this order: bass, vocal1, keyboard, drum, vocal 2.
I think this hits Standard 1, 2, 3, 4, 9.