Curving grades in introductory science courses is a common practice, with approximately half of chemistry and physics professors and one-quarter of biology professors reporting that they grade on a curve (Goubeaud, 2010). Proponents argue curving accounts for changes in the difficulty of exams, guards against grade inflation, and is a tool for ranking students and evaluating potential for graduate school (Sadler, 2005). However, critics argue that curving grades does not provide a valid measure of the degree of content mastery (Goubeaud, 2010). Despite the contentious debate over whether curving student grades is a valid assessment strategy, little empirical research has examined this practice. We will present the results of our study which examined the effects of curving introductory chemistry grades at a large, four-year university using data from over 16,000 students enrolled between 2008 and 2013. Hierarchical linear modeling was used to model students’ chemistry course grades as function of individual- and class-level characteristics. Results indicate that students’ grades were associated not only with their own prior achievement, but also with the prior achievement of students in their class. Being in a class with students who scored higher on the SAT and chemistry placement exam was associated with a decrease in student grades. This suggests that, as a result of curving, student grades are not representative of their own competency.Because the distribution of students varies substantially across classes, curving artificially deflates students’ grades in higher-achieving classes and inflates grades in lower-achieving classes.
Goubeaud, K. (2010). How is science learning assessed at the postsecondary level? Assessment and grading practices in college biology, chemistry and physics. Journal of Science Education and Technology, 19(3), 237-245.
Sadler, D. R. (2005). Interpretations of criteria‐based assessment and grading in higher education. Assessment & Evaluation in Higher Education, 30(2), 175-194.
