I teach at a Catholic school. We pray at the beginning of every class.
The first test I gave my first year, my students told me they were nervous. So I grabbed my computer and looked up the patron saint of test takers. It's St. Joseph of Cupertino. So we always said a prayer for his intercession before tests.
This year I kicked it up a notch and made a poster. I made it using PicMonkey, so it is a picture file. Feel free to use it in your classroom!