Want a quick way to know if your students are learning during an activity? I use the "Message Center" activity in Stationery Studio (with slight modification) for use in my room. Below you will see the note I use. I have a few hundred of them printed and in my desk drawer at all times. Whenever I want a quick idea if students have grasped a concept, I hand each one of them a message sheet and have them send me a memo. A lot more real than giving a pop quiz and takes only a few seconds!
Also, when I have my high school kids listen to a recording of the choir sing, I sometimes give them these notes and have them send a message to their section or to the whole choir. Great feedback and the fact that it comes from their classmates is very effective.