This report is about conceptual and methodological issues that arise when educational researchers use data from large-scale, survey research studies to investigate teacher effects on student achievement. In the report, we illustrate these issues by reporting on a series of analyses we conducted using data from Prospects: The Congressionally Mandated Study of Educational Opportunity. This large-scale, survey research effort gathered a rich store of data on instructional processes and student achievement in a large sample of U.S. elementary schools during the early 1990s as part of the federal government's evaluation of the Title I program. We use data from Prospects to estimate the "overall" size of teacher effects on student achievement and...