Only half of SAT-takers retake the exam, with even lower retake rates among low income and underrepresented minority (URM) students. We exploit discontinuous jumps in retake probabilities at multiples of 100, driven by left-digit bias, to estimate retaking's causal effects. Retaking substantially improves SAT scores and increases four-year college enrollment rates, particularly for low income and URM students. Eliminating disparities in retake rates could close up to 10 percent of the income-based gap and up to seven percent of the race-based gap in four-year college enrollment rates of high school graduates.