Background: The purpose of this study was to determine whether there was an association between dietary patterns and children's academic performance. Methods: This cross-sectional study involved 315 children aged 9-11 years from 26 schools in Australia. Academic performance was measured in 4 domains (reading, writing, numeracy, and language--subdomains: spelling, grammar, and punctuation) using the National Assessment Program in Literacy and Numeracy (NAPLAN). A self-reported child questionnaire collected dietary intake data. "Core" (healthy) and "noncore" (unhealthy) dietary patterns were derived using principal components analysis. Results: The noncore pattern was associated with lower NAPLAN scores across all academic domains (mean: -12.6, 95% CI: -18.7 to -6.4, r[superscript 2] = 0.073, p < 0.001) except writing, while the core foods pattern was not associated with NAPLAN scores across all domains. When the noncore model was adjusted for sociodemographic covariates (child body mass index, ethnicity, sex, parental education, household income, marital status, mother's employment hours, and number of siblings), the association was attenuated but remained statistically significant (NAPLAN summary score: -8.5, 95% CI -15.0 to -1.9, r[superscript 2] = 0.123, p = 0.011). Conclusions: Academic performance was deleteriously associated with a nutrient-poor, energy-dense diet, yet not associated with a nutritious diet.