This article examines the relationship between teacher effectiveness and students' achievement as measured by test scores. A strong belief among policymakers and public as well as private funding agencies is that test scores are directly related to the quality of teaching effectiveness. This relationship implies that there could be a direct causality among teacher preparation, teacher quality, and student achievement. The terms "teaching effectiveness" and "teacher effect" are often used interchangeably in these conversations. This article discusses several aspects of each construct, particularly: (1) teacher effects; (2) teaching or teacher effectiveness; and (3) an educational model of school and teacher effects on student achievement. Fundamental research issues and concerns as well as an alternative conceptual framework for studying the relationship of achievement and teaching are highlighted. (Contains 1 figure.)