During a session at SHAPE Boston, presenters Brian Devore (@bdevore7), John Jones (@JohnJonesPE), and Henry Castelvecchi (@PE4YOU) shared this terrific resource: http://nfhslearn.com/courses (You do have to register to take courses.)
If you select "student" and "free" on the left side you can browse the options available for your athletes/students.
One terrific idea would be to have your athletes, at the beginning of the season, complete the "Social Media for Students" course. If you are using Google Classroom with your team, you can create an assignment and include the link to the class: http://nfhslearn.com/courses/61062/social-media-for-students. When students complete the course, they would "Add" the screenshot file (showing completion of the course) to the assignment in classroom and "turn in".
There are many additional courses that you may want to require of your athletes/students.
Bullying, Hazing and Inappropriate Behaviors
Concussion for Students
Many thanks to Brian, John, and Henry for sharing this terrific resource!