Cognitive flexibility requires processing multiple sources of information and flexible adaptation of behavioral responses. Poverty negatively impacts cognitive control in young children, but its effects on infants are not well-understood. This study investigated longitudinally the development of cognitive flexibility in low-income infants. Thirty-two infants (15 low-SES, 17 high-SES) were tested at 6, 9, and 12 months of age. Cognitive flexibility was measured with a perseverative reaching task, where infants were taught to reach to one location and then asked to switch to a second location. High-SES infants replicated the typical developmental trajectory, reaching randomly at 6 months, perseverating at 9 months, and reaching correctly at 12 months. In contrast, the low-SES infants showed a delayed pattern, reaching correctly at 6 months, randomly at 9 months, and perseverating at 12 months. Links between cognitive flexibility and frontal cortex development are explored as a potential mechanism.