The current study tests if the type of children's daily main meal (slow versus fast food) mediates the association of socioeconomic status (SES) with cognitive ability and cognitive growth in childhood. A Scottish birth cohort (Growing Up in Scotland) was assessed at ages 3 (N = 4512) and 5 years (N = 3833) on cognitive ability (i.e. vocabulary and picture similarities), SES, and the frequency of having slow and fast food main meals per week. SES was highly correlated at ages 3 and 5 years, while intelligence and the type of meal were only moderately associated across ages. SES at age 3 was positively related to ability at age 3 but not at age 5. The type of meals partially mediated the effects of SES on cognitive ability at ages 3 and 5, with more slow meals being associated with better cognitive performance. Furthermore, a higher frequency of slow food meals were positively related to cognitive growth between ages 3 and 5 years, after adjusting for SES and prior cognitive ability; however, they only accounted for a negligible amount of the variance in cognitive change. Overall, slow food was associated with better cognitive ability and cognitive growth in childhood, albeit corresponding effect sizes were small. (Contains 7 tables and 2 figures.)