The effectiveness of schools and the levels of investment in schooling have been in question since the 1966 Coleman report "Equality of Educational Opportunity." Based on a theory of "knowledge-ability," this study challenges the assumption that given "inputs" will yield equivalent effects or "outputs." In this study, 120 elementary schools were randomly selected, and questionnaires were mailed to the principals eliciting background data on the school, its pupil population, resources, and faculty. Each principal was asked to identify the three "most outstanding" teachers in the third-, fourth-, and fifth-grade levels. The teachers were mailed questionnaires and inventory checklists of approved instructional practices that represent tested pedagogical techniques supported by authorities and research evidence. The extent to which approved practices were reported being utilized provided some measure of the level of knowledge-ability of the teachers. The variation in teacher knowledge-ability within schools was found to be considerably greater than the interschool differences in knowledge-ability. In conclusion, the authors suggest that the study of knowledge-ability of teacher populations rather than of schools will likely be a more productive avenue for improving the effectiveness of schooling. (Author/MLF)