Student performance, attrition, and class size given missing student data

Class size is of particular interest to education researchers and administrators because it is one of the few variables that administrators can change from term to term. In studies of class size, however, little if any attention is given to the consequence of missing student records that result from “data cleaning” done by those collecting the data, student unwillingness to provide data, or students self-selecting out of the study and the implications of this selection on an appropriate measure of class size. These shortcomings are addressed here: class size and other class-specific variables that may affect student learning of economics are considered along with the hazard of attrition between the pre-course test and the post-course test and students' failure to complete questionnaires about themselves and the courses. Contrary to studies that have used an average or an end-of-term class size measure and find no class-size effect, beginning class size is found to be significant and negatively related to learning of economics, all else equal. In part, this is the result of students in larger classes being significantly more likely than students in smaller classes to withdraw from the course before taking the posttest.