The component processes of complex planning follow distinct developmental trajectories

Developing the ability to plan is an important part of children’s transition into independent adults. Characterizing the development of planning ability in complex environments has been a longstanding interest in developmental science. Complex planning is known to involve multiple cognitive processes that enable the representation of the problem domain and the simulation of potential futures. To date, however, we lack a mechanistic account of how complex planning ability develops, in large part because prior developmental research has relied on tasks with small state spaces and analysis approaches that cannot effectively disentangle how multiple, distinct cognitive processes contribute to planning. Here, we address these shortcomings by leveraging a game-like planning task and a corresponding computational modeling framework, previously used in adults, to delineate the developmental trajectories of three component processes of complex planning. These processes include heuristic evaluation of prospective states based on relevant features, forward simulation of potential future actions and their outcomes (i.e., planning depth), and sustained attention to relevant features. Participants (ages 8-25 years) played the Four-in-a-row task, presented as a 4x9 board game, against computer opponents. This task assesses complex planning as it has too many potential future scenarios to exhaustively consider, a feature of many real-life planning scenarios. We found asynchronous age-related change in the component processes of complex planning, with the heuristic evaluation of relevant features rapidly improving from childhood into adolescence, and planning depth showing more protracted developmental improvements. Fewer attentional oversights predicted better planning but did not demonstrate age-related variability. Collectively, these results provide strong evidence for the continued development of model-based decision strategies into adulthood, and contribute to a more nuanced understanding of the cognitive mechanisms underpinning planning ability within complex environments at different developmental stages.