A book that I read over spring break that has since guided my approach to whole group instruction is
Total Participation Techniques: Making Every Student an Active Learner by Persida Himmele and William Himmele. They make the point that if only a few students raise their hands and participate in class discussions, then you only know if those few are learning the material. After spring break I started explicitly pairing up students for buddy talks, and each pair got a white board. Several time during the lesson, I ask the students to talk over a problem/idea with their shoulder buddy, and then write their answer on the white board. I don't proceed until every white board has something written on it.
Did it work? Once the kids believed I wouldn't continue till every white board had something written on it, the kids did write on the white boards. If I put myself in their position, such a requirement would irritate me if the question itself wasn't engaging -- and that's the challenge. Some of the kids did discuss more with their partners, and others just wrote on the board without discussion.
