Abstract
Neurodevelopmental disorders are defined within a developmental framework, yet diagnostic reasoning in clinical practice still relies largely on observations made at a single time point. This creates a tension: intervention is expected early, while diagnostic validity depends on how difficulties evolve over time. We argue that this tension reflects a limited integration of time into diagnostic reasoning. In the absence of validated biomarkers, clinical manifestations are not static. They emerge from interactions between brain maturation, environmental demands, and compensatory processes. Their meaning depends on how they change over time and respond to intervention. This perspective calls for a better account of developmental variability and the heterogeneity of trajectories, particularly in childhood. During this period, expectations change rapidly, and differences in maturation may lead to divergent interpretations of similar behaviors. Executive functions are discussed as one illustrative developmental marker because of their prolonged maturation, transdiagnostic nature, and sensitivity to contextual demands. Diagnosis is therefore better understood not as a one-time decision, but as a process grounded in developmental trajectories. Longitudinal observation, including repeated assessments and changes in response to structured environmental adjustments, provides critical information to distinguish transient developmental difficulties from more persistent neurodevelopmental constraints. This framework has implications for both clinical practice and research. It supports early identification and intervention, while emphasizing the need for structured longitudinal monitoring and stronger integration of temporal dynamics into diagnostic models. In neurodevelopment, diagnosis is not the reading of a state, but the interpretation of a trajectory.