The assumption that delayed brain development universally characterizes attention disorders may be fundamentally flawed, overlooking critical sex-based differences that could reshape how clinicians understand and treat ADHD in young people. This oversight has potentially led to misdiagnosis and suboptimal treatment approaches for millions of children and adolescents. The PNAS investigation tracked cortical thinning patterns across thousands of youth over multiple years, revealing that the widely cited 'delayed maturation' biomarker for ADHD shows dramatically different patterns between males and females. Previous smaller studies suggesting universal developmental delays in attention disorders failed to account for these sex-specific trajectories, leading to oversimplified clinical models. The research demonstrates that cortical development in attention-challenged youth follows distinct pathways depending on biological sex, with timing, regional specificity, and progression rates varying significantly. These findings challenge the one-size-fits-all approach currently dominating ADHD research and clinical practice. From a broader neurodevelopmental perspective, this work aligns with emerging evidence that sex differences in brain maturation extend far beyond reproductive systems, influencing cognitive development, psychiatric vulnerability, and treatment responsiveness. The implications for personalized medicine are substantial, suggesting that effective ADHD interventions may need sex-stratified approaches rather than universal protocols. However, the observational nature of this study cannot establish whether these developmental differences cause attention problems or represent compensatory responses. The research underscores a critical limitation in decades of neurodevelopmental research that treated sex as a secondary variable rather than a fundamental biological factor shaping brain development trajectories.