PracticeCactus has been published to the Google Play store. The app has 3 main features to support piano learners: sharing, listening, and self-tracking. Additional features which can be enabled by the piano teacher include a digital dictation book, and embedded technical exercises, by grade level. Create a teacher account at thepracticecactus.com
EDIT: The app is not currently working. If you are interested in using PracticeCactus, as a teacher, parent, or student, please fill out the following form. You will receive an email when your version of PracticeCactus is up and running. Thank-you for your interest!