Today's lesson on nerve cell action potentials was one of those lectures where for no single apparent reason everything just clicked. Every portion of the lecture seemed to seamlessly flow together, the students were involved the entire time and asked many more questions than usual, and by the end of the period it was clear from their questions that at least a decent number of the students had a firm grasp of the basics of action potentials. It was a very, very enjoyable hour and a half.
Near the end of the lecture I asked a few in-class response system questions about what would happen if we changed ion concentrations around a neuron. The first question was easy (removing sodium ions from the system), while the second was harder (adding extracellular potassium, difficult partially because I hadn't discussed potassium in depth by that point). About 65% of the class got the first question correct on the first try, but for the second question only 19.5% of the class (22 students) chose the correct answer.
I was originally planning on conducting a class discussion on the second question, but after seeing the low success I decided to have the students get into groups and continue working on the problem (there'd been very little interaction initially). I gave the students another 4 minutes, and during that time it seemed like the majority of the class was actively discussing the problem. After working in groups the percentage of students choosing the correct answer nearly doubled to 38.5% (41 students), and a few people were able to easily explain the mechanism underlying the answer in detail.
This question series seems like a good example of the potential power of group work (though there are clearly far better studies on the topic), as well as the quick data collection and classroom management benefits you can get using in-class response systems.