The Order-Processing Questionnaire (OPQ) is a parental-report measure designed to assess children’s everyday ordering abilities, which may be an indicator of early mathematical difficulties. This study aimed to replicate and validate the OPQ’s two-factor structure previously identified by O’Connor et al. (2018) using a larger sample of parents of first year primary school children in Northern Ireland. Confirmatory factor analysis replicated the factor structure found in O’Connor et al., with moderate-to-strong factor loadings, but indicated mixed results regarding model fit. Reliability was acceptable for the Positive Item factor but weaker for the Negative Item factor, likely due to the smaller number of items. There was evidence of stronger discriminant and convergent validity for the Positive Item factor. Findings highlight the OPQ’s potential as a tool for identifying early mathematical difficulties but underline the need for further refinement, particularly with regards to item phrasing and establishing predictive validity.