Teachers: Automate class attendance by having your students "check in" with their phones.
You: Make an account at https://youhere.org, and create a class. Set your attendance requirements, such as your classes (GPS) location and meeting times.
Your students: Each installs this app on their phone and tells it about your class. Thereafter, they use the app to 'check in' to your class.
The app uses the phone's location capabilities to see if they're in the right place at the right time (according to your attendance requirements). Results are logged to your Youhere.org account.