An experiment in "re-quizzing"

I did an interesting "experiment" with the students in my general chemistry II class this last week.  In that class I give weekly low-stakes quizzes and the students did very poorly on the last one I gave.  I decided to post the key and notified the students that they would be doing a quiz "re-do" the next class period where I would be giving them select questions from the quiz off the key (with the answers) and their task would be to build explanations for the answers.  I was pleasantly surprised by the buzz it created around trying to understand the answers on the key and the re-quiz results were dramatically better.  These were fundamental concepts I value in the class and felt that after this quiz-answer key analysis-requiz experience the students had a much better understanding of the ideas.

I have been trying out different assessment models in order to try to make them learning experiences for the students.  Along with the 80/20 group testing I have implemented (an idea I got from Susan Jorstad), this one was a success.