Methods for Accounting for Co-Teaching in Value-Added Models

ii ABSTRACT Isolating the effect of a given teacher on student achievement (value-added modeling) is complicated when the student is taught the same subject by more than one teacher. We consider three methods, which we call the Partial Credit Method, Teacher Team Method, and Full Roster Method, for estimating teacher effects in the presence of co-teaching. The Partial Credit Method apportions responsibility between teachers according to the fraction of the year a student spent with each. This method, however, has practical problems limiting its usefulness. As alternatives, we propose two methods that can be more stably estimated based on the premise that co-teachers share joint responsibility for the achievement gains of their shared students. The Teacher Team Method uses a single record for each student and a set of variables for each teacher or group of teachers with shared students, whereas the Full Roster Method contains a single variable for each teacher, but multiple records for shared students. We explore the properties of these two alternative methods and then compare the estimates generated using student achievement and teacher roster data from a large urban school district. We find that both methods produce very similar point estimates of teacher value added. However, the Full Roster Method better maintains the links between teachers and students and can be more robustly implemented in practice.