Literacy and numeracy are correlated throughout development, however, our understanding of this relation is limited. We explored the predictors of literacy and numeracy covariance (i.e., shared fluency between literacy and numeracy) in children (N = 1167, girls = 563) in rural Côte d'Ivoire, with specific focus on how developmental timing of instruction may relate to covariance. Many Ivorian children experience late enrollment and grade repetition, leading to variation in age-for-grade; participants were between grades 1 to 6, but their ages ranged from 5 to 15 (M = 9.19, SD = 2.07). Phonological awareness, numerical magnitude, ordinality, working memory, and inhibitory control were cognitive predictors of covariance. Age-for-grade was negatively related to covariance suggesting that covariance is related to timing of instruction.