Abstract Background Most studies of associations between child growth and cognitive ability were based on size at one or two ages and a single measure of cognition. We aimed to characterize different aspects of early growth and their associations with cognitive outcomes in childhood through adolescence. Methods In a sample of 12 368 Belarusian children born at term, we examined associations of length/height and weight trajectories over the first 6.5 years of life with cognitive ability at 6.5 and 16 years and its change over time. We estimated growth trajectories using two random-effects models—the SuperImposition by Translation and Rotation to model overall patterns of growth and the Jenss-Bayley to distinguish growth in infancy from post infancy. Cognitive ability was measured using the Wechsler Abbreviated Scales of Intelligence at 6.5 years and the computerized NeuroTrax test at 16 years. Results Higher length/height between birth and 6.5 years was associated with higher cognitive scores at 6.5 and 16 years {2.7 points [95% confidence interval (CI): 2.1, 3.2] and 2.5 points [95% CI: 1.9, 3.0], respectively, per standard deviation [SD] increase}. A 1-SD delay in the childhood height-growth spurt was negatively associated with cognitive scores [–2.4 (95% CI: –3.0, –1.8) at age 6.5; –2.2 (95% CI: –2.7, –1.6) at 16 years]. Birth size and post-infancy growth velocity were positively associated with cognitive scores at both ages. Height trajectories were not associated with the change in cognitive score. Similar results were observed for weight trajectories. Conclusions Among term infants, the overall size, timing of the childhood growth spurt, size at birth and post-infancy growth velocity were all associated with cognitive ability at early-school age and adolescence.