Assessing Definitional Competence: Construction, Validation, and Applications of the Co.De. Scale.

Definitional competence involves the ability to understand and produce definitions of different kinds of words. The Co.De. Scale was developed to systematically assess this skill across age groups, emphasizing both linguistic form and semantic content. This study aimed to provide normative data for the Italian population and validate the Co.De. Scale in terms of its validity, reliability, and responsiveness. A sample of 2262 participants aged 3-62 years from various regions in Italy was assessed using the Co.De. Scale, and age-stratified percentile norms were derived. Dimensionality and construct validity were examined through parallel analysis, confirmatory factor analyses comparing different models, an item response theory model, and measuremen-invariance analyses across gender and age-group; convergent validity was examined though associations with linguistic and cognitive measures. Reliability was evaluated via internal consistency and inter-rater agreement, and responsiveness via pre-post changes in an intervention study. Definitional competence showed a clear developmental progression, with significant effects of age and education levels. Bifactor indices supported an essentially unidimensional structure, which was fully invariant across gender but-consistent with a developing ability-not across age groups. The scale showed excellent internal consistency, high inter-rater agreement, significant correlations with related constructs, and sensitivity to intervention-related change. The Co.De. Scale is psychometrically sound tool for assessing definitional competence from preschool to adulthood. Its applications in educational, clinical, and research settings, combined with its ability to capture developmental changes, underscore its value for understanding and enhancing linguistic and cognitive development.