This report describes variables that differentiate the classrooms of more effective and less effective teachers. Teacher effectiveness is defined as the ability of second- and fifth-grade teachers to teach specially constructed reading and mathematics curriculum units over two weeks. Twenty more effective and twenty less effective teachers were visited for five days by specially trained ethnographers. Protocols of reading and mathematics instruction were prepared by the ethnographers. These protocols were rated, and variables that distinguished between teachers of differential effectiveness were identified. Twenty-one of these variables were found to distinguish between the more effective and the less effective teachers in their teaching of second-grade reading, second-grade mathematics, fifth-grade reading, and fifth-grade mathematics. An additional 40 variables also showed some ability to differentiate between more effective and less effective teachers, but did not generalize across grade levels or subject matter areas. The use of a known sample of teachers varying in effectiveness and the ethnographic procedures were both methods found to be very useful in the study of classroom teaching. (Authors)