The primary goal of this study was to examine whether effortful control (EC; effortful regulation), reactive undercontrol (IMP; e.g., impulsivity, speed of approach), and reactive overcontrol (NOV; inhibition to novelty) were 3 distinct constructs at 30 months (Time 1; n = 216), 42 months (Time 2; n = 192), and 54 months (Time 3; n = 168) of age. Parents', nonparental caregivers', and/or observers' ratings were obtained for all 3 constructs at all 3 times, as were multiple behavioral indices of each construct. Several alternative factor structures were tested, including 1-, 2-, and 3-factor models. The best fitting and most parsimonious model was one with 3 separate latent constructs at 42 and 54 months and 2 distinct constructs, EC and impulsivity/low inhibition to novelty combined, at 30 months. EC, IMP, and NOV also demonstrated some interindividual consistency across time, especially EC and IMP.