The Wave is very loosely based on a situation that went down in Palo Alto, California in the 1960s.
Todd Strasser isn't that famous in the U.S. But in Germany, where he's known as Morton Rhue, he's a household name. His books, especially The Wave, are required reading in many German schools. (Source.)
Our author is super involved with the young adults who read his books. He makes a ton of trips to different schools to speak, and even Skypes with some classrooms! (Source.)
This real-life story isn't the only one of its kind. Check out the Stanford Prison Experiment for another example of an experiment gone wrong.