Specific, measurable, attainable, relevant, and time-based. You know, all that stuff you're sitting through discussing in your PD sessions right now.
I've had good success with asking for a two-octave chromatic scale. Some kids can play the p*** out of that day one - some don't even know half the notes of the scale yet. That lets you tier your students and results appropriately.
Test them first in September, again in January, and for a final time in April after UIL.