Comprehensive Psychometric Evaluation of the Assessment of Basic Language and Learning Skills‐Revised and the Assessment of Functional Living Skills

ABSTRACT Neurodevelopmental disabilities, including autism spectrum disorder, have increased in prevalence, highlighting the need for reliable and valid instruments that guide behavioral interventions. This study reports a comprehensive psychometric evaluation of the Assessment of Basic Language and Learning Skills–Revised (ABLLS‐R) and the Assessment of Functional Living Skills (AFLS). Strong unidimensionality, adequate or better reliability, and good convergent and known‐groups validity were hypothesized across content areas. Using assessment data from 41,912 unique individuals (89,733 total administrations), multiple reliability and validity analyses were conducted. Most content areas showed unidimensionality, excellent internal consistency ( α ≥ 0.88), and fair to excellent test–retest reliability (all ABLLS‐R r xx ≥ 0.40 and all AFLS r xx ≥ 0.60). The correlation between ABLLS‐R and AFLS total scores was high ( r = 0.82). Known‐groups validity was supported, with expected differences between individuals with and without intellectual disability. Results demonstrated that the ABLLS‐R and AFLS have strong psychometric properties, supporting their utility in intervention planning and progress monitoring.