The following resources can help you plan projects and activities with GarageBand:
This is an e-book created by Apple. Each Chapter shares activities and projects you can do with GarageBand while also teaching the different parts of GarageBand. They are not all related to contemporary music making but can give you ideas of how you can have students take advantage of the varied aspects of GarageBand on the iPad.
This is an e-book designed for teachers to help facilitate the activities from the Everyone Can Create Music (for iPad) book.