Purpose The association between nutrition and cognitive test performance among school children is limited in developing countries, including Ghana. This paper aims to investigate the relationship between nutrient intake and cognitive competence in the context of abstract reasoning among school-aged children in the Tamale Metropolis. Design/methodology/approach The present cross-sectional study recruited 596 children aged 9–13 years from government-owned and private primary schools in Tamale Metropolis. Dietary intake was assessed by using three-day repeated 24-hour recall. Cognition was assessed by the Raven’s Coloured Progressive Matrices (RCPM) test, made up of 36 questions and used as a continuous variable, whereby higher scores indicated better cognition. Findings The majority of the children did not meet the recommended dietary allowances for protein (55.5%) and fibre (94.0%) and estimated adequate requirement for energy (86.6%), folate (72.8%), vitamin E (90.6%) and zinc (74.8%). More girls (55.1%) performed poorly in the cognition test than the boys (45.7%) (p = 0.029). Between-subject effects determined using univariate and multivariate analyses indicated age (p = 0.002), dietary folate (p = 0.016), vitamin C intake (p = 0.011), combined age and dietary folate (p = 0.049) and combined age and dietary vitamin C (p = 0.022) significantly affected cognition scores. Girls had lower odds (AOR = 0.7, p = 0.021, 95%CI = 0.5–0.9) of scoring above the 50th percentile in cognition test than boys. Research limitations/implications The current nutrient intakes of the children were inadequate. The children performed poorly in Raven’s cognition test of abstract reasoning, and this was associated with being a girl. Originality/value To the best of the authors’ knowledge, this study is the first to investigate nutrient intakes and RCPM test performance among children in Northern Ghana. Thus, the findings of the study provide relevant information needed by stakeholders to implement nutrition programs in basic schools, aimed at ensuring optimal nutrition achievement among school children for improved cognition.