The lessons seemed to be geared more for the elementary crowd but a number of ideas could easily be adapted for older students. Easy to lead discussion starters are a highlight that pose scenarios and ask learners what they would do.
Topics include online bullying and taking personal responsibility for appropriate use of a technology. A fun culminating activity is the blank template for students to create their own Safer Internet Day poster. There are also additional classroom posters and resources you can print and keep up all year.
Don't worry if you can't cram any of this stuff in today, the official Safer Internet Day. With these resources you can make everyday Safer Internet Day. Isn't that how it should be anyway?
Update: A ton more great resources from Better Internet for Kids, the parent organization behind Safer Internet Day.