Tynker is a service that offers programming lessons for elementary school and middle school students. I published a full overview of the service a couple of days ago. You can read that overview here. For Pi Day Tynker is offering a free lesson plan in which students practice their programming skills by making art based on Pi.
Tynker's Pi Day lesson plan has students use Tynker's block programming interface (available to use in your web browser or on Tynker's iPad app) to create art and animations featuring the digits of Pi.
Applications for Education
Tynker's Pi Day lesson plan includes nine pages of step-by-step directions. Despite those detailed directions, if you have never done any programming with your students, I wouldn't make the Pi Day project your first attempt at programming with students. But if you and your students are already familiar with Tynker then the Pi Day lesson could be a fun one for you to use.