What was the third motto that Mr. Ross taught his class in The Wave?

When Mr. Ross' ill-fated experiment begins, he comes up with two slogans for his students to use: "Strength through Discipline" and "Strength through Community." These will form the basis of The Wave's ideology, to be repeated over and over again parrot fashion as a means of ensuring group solidarity. In addition to the slogans, Mr. Ross also devises a symbol for the new group—a circle with the shape of a wave in it—and a salute.
As The Wave begins to take over the campus, it starts intimidating other students. The Wave is no longer an abstract idea, or a thought experiment, but a living, breathing movement. That being the case, there needs to be another slogan, one that encapsulates The Wave's commitment to making other students bend to its will. So as well as the other two slogans we now have "Strength through Action."