This paper presents one researcher's premise that the most important variable in determining classroom effectiveness is the congruence of the delivered curriculum with the desired outcomes or, that students be given the opportunity to learn what is expected of them. This theory presupposes that curriculum expectations be made clear to students, and that students be given sufficient time and resources to achieve those expectations. The role of administrators is therefore to make these expectations clear to teachers, to provide teachers with the means to carry them out, and to assure that teachers do carry the goals out. Teachers and administrators must share a common belief that certain outcomes are expected for students at a given grade level in a given school. Evaluation devices must also be geared precisely to these specific curricular goals. Three important related concepts are defined and discussed: allocated time, engaged time, and success rate. These concepts are then brought together into a single concept of academic learning time, defined as engaged time with materials or activities that produce a high success rate and are related to outcome measures. This concept of academic learning time is shown to be a good predictor of classroom effectiveness. The paper concludes with general observations on the utility of research in assessing teacher effectiveness. (TE)