It is an American RadioWorks documentary and well worth the listen (it is about 53 minutes long) for all middle school, high school, and college math teachers.
The instructors interviewed are physics professors, but most of the ideas apply to math instruction too.
Some of the recommendations:
Students read the material before class so are prepared to engage in discussions and ask questions about points of confusion.
Students get designated time to study and solve problems together. (Furthermore, I encourage the formation of study groups outside of class time, especially before exams.)