Drawing on Geary's (1995) evolution-based model of cognitive and academic development, this study investigated the relation between biologically primary skills (vocabulary, executive functions, and visual-spatial processing) and subsequent word reading and calculation. It also examined the extent to which these relations were mediated by biologically secondary skills (metalinguistic awareness and symbolic numerical processing). A total of 197 Chinese children (age at the first measurement point: M ± SD = 53.38 ± 3.32 months) were assessed three times over 18 months on their vocabulary, spatial perception, working memory (WM), short-term memory (STM), inhibitory control, metalinguistic awareness (i.e., phonological awareness, morphological awareness, and orthographic awareness), symbolic numerical skills (i.e., counting, number comparison, and number transcoding), Chinese word reading, and calculation competencies. The results showed that STM and spatial perception predicted subsequent calculation after baseline performance and background information were controlled for, and the contributions were fully mediated by counting and number transcoding. Inhibitory control had a direct effect on later calculation, which was not mediated by any secondary skills. With regards to word reading, although none of the biologically primary skills predicted later word reading after controlling for baseline performance and background information, vocabulary; spatial perception; STM, inhibitory control; and WM had indirect effects on word reading via phonological awareness, orthographic awareness, and number transcoding. Implications for theory and practice are discussed.