Amazingly enough, Hands and Eyes works as well with high school students as with kindergartners.  In actual practice, you will use Class-Yes anywhere from 20 to 30 times an hour, especially when you are involved in direct teaching and Hands and Eyes about 5 to 10 times. 

"Mirror my gestures," is also a very useful command.  As you teach with gestures, you will know who is engaged in the lesson simply by seeing who is copying your hand motions.  A more advanced version is to say, "Mirror!" and your students respond "mirror!" and snap their hands into the air, ready to mimic your gestures.  In the critical thinking Power Teacher video (click on Power Teacher videos), Jay Vanderfin's class does an excellent job of demonstrating this technique.