From Developmental Timing to Clinical Visibility: An Integrative Narrative Review of Sex-Related Neurocognitive Development.

Research on sex-related differences in child and adolescent neurocognitive development has often been framed around whether boys and girls differ and which group performs better. This framing is increasingly inadequate because it treats developmental timing, observable phenotypes, and clinical recognition as interchangeable forms of evidence. Drawing on developmental neuroscience, cognitive development, research on gendered experience, and clinical studies of autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD), this integrative narrative review proposes a developmental-visibility framework. The framework interprets sex-related differences across three analytically distinct layers: developmental timing, phenotypic expression, and clinical recognition. Developmental timing refers to age-related trajectories, pubertal coupling, maturation tempo, and variability. Phenotypic expression refers to how developmental differences may appear in language, executive function, emotion, and social cognition under specific task and measurement conditions. Clinical recognition refers to how informants, referral thresholds, compensatory or camouflaging behavior, and diagnostic tools influence which difficulties are identified. ASD and ADHD illustrate the clinical-recognition layer because less externally disruptive or more compensated presentations may remain underrecognized despite meaningful developmental burden. The framework helps explain why modest average effects, inconsistent behavioral findings, and unequal clinical recognition can coexist. It shifts the field from asking whether sex-related differences exist to asking when, how, and under what social and clinical conditions they become visible.