Here's another great idea for motivating and tracking practice! Pianoanne posted a review of the PractizPal electronic device. It's a metronome, timer, and practice journal all in one. Boy oh boy, would my kids love one of these! Actually it would have to be 3 of these because they are designed as a personal electronic device meaning they only track practice for one person.
So go check out the review at Pianoanne and you can enter her giveaway (except don't because I would love to win it myself ;).