The dual systems model of adolescent development asserts that the neurobiological systems underlying reward/motivational processes and cognitive control mature at different rates, resulting in an "imbalance" during adolescence whereby adolescents are biased toward rewards but unable to exert sufficient executive control in risk-taking contexts. While a hypothesized imbalance between these systems is central to the dual systems model, few studies have investigated longitudinal trajectories within and between each system with age. Therefore, this validation study assessed the developmental trajectories of the reward and control systems, and directly quantified within-person differences between these systems using an accelerated longitudinal design, including up to five biennial assessments per participant. The sample included 166 predominately White individuals from middle-class to upper-middle-class backgrounds, aged 9-29 years, of which 54% were female at birth. Results indicate that both self-reported reward sensitivity and laboratory-based executive functions increase rapidly during early adolescence and plateau by early adulthood. Findings provide evidence for a unique period of developmental imbalance with heightened reward sensitivity relative to executive control present in early adolescence and imply that most adolescents demonstrate top-down regulatory control over incentive-reward motivation by mid-to-late adolescence. However, some individuals deviate from this mean-level trend, suggesting that individual differences in neurodevelopment must be considered as important determinants of decision-making in later adolescence. Further research into how developmental differences between reward and control systems relate to decision-making processes, including risk-taking tendencies, is an important future direction for this research. (PsycInfo Database Record (c) 2025 APA, all rights reserved).