Are All Gains from Supplemental Instruction Due to Selection Bias?

Alexa Prettyman (), Seth Gitter (), Melissa Groves (), Raquel Frye () and Lucienne Karszen
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Alexa Prettyman: Department of Economics, Towson University
Seth Gitter: Department of Economics, Towson University
Melissa Groves: Department of Economics, Towson University
Raquel Frye: Department of Economics, Towson University
Lucienne Karszen: University of Maryland Global Campus

No 2026-09, Working Papers from Towson University, Department of Economics

Abstract: Supplemental Instruction (SI), an academic support program that targets difficult introductory college level courses, is praised for increasing grades by half a letter grade. We rigorously evaluate SI in introductory economics and biology courses at a regional university in the mid-Atlantic. Students who attended SI review sessions were up to 65 percent less likely to earn a D, F, or W, and they earned higher grades by a full letter grade. However, participation in SI was low; only 14 percent of students attended multiple SI review sessions, and higher achieving students were more likely to attend sessions. Any increases in grades are concentrated among biology courses and high-achieving students. In conclusion, we find that grade improvements from SI are due to positive selection bias, with limited evidence of causality. While SI might be beneficial for some students, it is less clear whether this program is the most cost-effective approach for struggling students.

Keywords: Supplemental instruction; introductory economics; selection bias; causal inference. (search for similar items in EconPapers)
JEL-codes: A22 I20 I23 (search for similar items in EconPapers)
Pages: 45 pages
Date: 2026-05, Revised 2026-05
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