Three recent large-scale experimental studies have built on a data base established through several correlational studies of teaching effectiveness in elementary school. These three studies have in common a treatment that addresses several routine teaching tasks and suggests some principles and techniques for effectively fulfilling those tasks. All three studies yielded results indicating that the treatment teachers did use many of the behaviors suggested to them and that their students had higher adjusted achievement scores. In this article, the three studies are reviewed and suggestions are made about future experimental studies of teaching effectiveness. (Author/JD)