The first generations of researchers on classroom instruction were the pioneers who developed the term, categories, and concepts that were used to view and code what was happening during classroom lessons. The five pioneers in this first wave were Ned Flanders, Arno Bellack, B.O. Smith, Don Medley, and Harold Mitzel. Each of these pioneers used different sources and developed different terms and categories to code classroom events. As a result of the conceptual work of these pioneers and the increasing number of studies correlating classroom events with student achievement, researchers began to develop their own category systems and some of them conducted their own correlational studies. Jere Brophy was the most productive scholar in this second generation of researchers on teaching. This article will describe four of Brophy's major contributions: (1) The Brophy-Good Dyadic Observation Instrument (BGDOI); (2) Correlational and experimental studies; (3) Reviews of research; and (4) Students.