When that happens, we use the lesson for practice, and we do the repetitions in the lesson. To keep the interest and so that they don't quit piano the following week, I add variety to the repetitions:
It works wonders! Suddenly repetitions are not so boring. The students are laughing, experimenting and enjoying the learning process. It takes up quite a bit of time (especially when they get to change the voice and want to try out 10 of them before they choose one they like), but I end up with a group of super happy piano students who continue to "love piano class!"