Diagnosing specific learning disorder in adults Part I: conceptual and methodological challenges

INTRODUCTION: Specific learning disorders (SLDs) are widely conceptualized as lifelong neurodevelopmental conditions; however, the validity of first-time diagnosis in adulthood, particularly in postsecondary and professional settings, remains poorly defined. Despite more than six decades of research, the field lacks a stable definition and empirically validated diagnostic criteria capable of reliably distinguishing SLD from normative academic variability or contextual disadvantage. METHODS: Part I of this paper presents a critical narrative review of the historical development of the SLD construct, population prevalence estimates in adults, and the major diagnostic frameworks that have shaped identification practices. We examine evidence concerning IQ - achievement discrepancy models, Response to Intervention, Processing Strengths and Weaknesses approaches, and DSM-IV, DSM-5, and DSM-5-TR criteria, with attention to psychometric validity and diagnostic utility. RESULTS: The reviewed literature demonstrates persistent definitional instability, continued reliance on empirically unsupported discrepancy-based logic, and extreme heterogeneity in adult and postsecondary SLD samples. Diagnostic practices frequently classify individuals with average or above-average academic achievement as SLD, particularly in selective educational contexts. Evidence further indicates that adult SLD diagnoses and associated accommodations are disproportionately concentrated among socioeconomically advantaged students, raising concerns about construct drift, equity, and validity. CONCLUSIONS: Contemporary adult SLD identification remains insufficiently anchored to population-referenced academic impairment, developmental continuity, and objective evidence of functional limitation. These shortcomings undermine confidence in SLD as a neurodevelopmental construct. Part II examines the cognitive, professional, and institutional factors sustaining these practices and proposes a stepped, empirically grounded framework for diagnosing SLD in adolescents and adults.