Screening early numerical development in Brazilian children: adaptation and validation of MARKO-S.

Mathematical learning difficulties (MLD) are estimated to affect a substantial proportion of children worldwide, yet psychometrically validated screening instruments for early numerical development remain scarce in non-WEIRD countries, including Brazil. MARKO-Screening is a brief, theoretically grounded screening instrument designed to assess early numerical development in preschool and early elementary children. Based on a developmental trajectory model of numerical concept acquisition, MARKO-S evaluates foundational concepts including counting, ordinality, and cardinality. This study aimed to adapt and validate a Brazilian Portuguese version of MARKO-S (MARKO-S BR) for early identification of children at risk for MLD, examining evidence of content validity, internal structure, and relations with other variables in a sample of 1,200 children from preschool to second grade, enrolled in public and private schools across three Brazilian regions. Results provided evidence of structural validity, with item difficulty largely aligned with the theoretical model, and convergent validity through positive correlations with established mathematical assessments. MARKO-S BR scores showed significant grade-related differences, consistent with the expected acquisition of numerical concepts across schooling. Substantial performance gaps also emerged between public and private school students, reflecting systemic inequalities in early mathematics education in Brazil. These findings support MARKO-S BR as a psychometrically sound, culturally adapted screening instrument, addressing the scarcity of validated early mathematics assessments and providing Brazilian educators and clinicians with an evidence-based digital tool for early identification of children at risk for MLD.