Today we spent almost all class Whiteboarding in my on AP class. We were practicing the chain rule by rewriting functions with different colors for the inside and outside functions, then taking the derivatives using different colors to indicate where things came from. We did this for about 30 minutes straight. Students generally love working on whiteboards, but I noticed after about 20 minutes students starting to lose focus and need reminders to get back to work, which has never happened so widely in this class. It made me remember how important it is to chunk class into meaningful but manageable pieces. The only reason why it's bad to lecture for 45 minutes is because you are doing the same thing for 45 minutes! Doing the same thing with a more interactive learning mode is just as bad. Point taken.