Most of today was a test. But, the best part was whiteboarding our answers to the double-slit questions. We got confused about what would happen when the two sources were brought closer together. We couldn't really communicate, so I got the great idea to get two tape measures to act as the two sources. We could see the path length difference, and when the two people moved closer together, we could see how we had to change where we were measuring the path length difference to keep the "one wavelength" difference (of 25 centimeters). I recommend this demonstration.
To me, it was a reconfirmation. If a student asks a question, more and more, my gut says "let's try it out" rather than "let's reason it out" or "let me tell you." It's the best change in my teacher I've ever made.