Practice charts

Yes it is "old school" but I swear, practicing charts really work. They are simple and can be picked up at any music store. My children have to practice 5-6 days per week and get 1 star for every day. One row of stickers = 1 point. They can choose to spend that point at the "practice store" or save it for something bigger when they've earned more points. 1 point will get you something like an eraser and 10 points will get you a journal (or something similar.) This concept is great because it not only rewards them for practicing but teaches them the value of saving.