How early reading, mathematics, and cognitive skills mutually support each other in kindergarten through second grade

Early literacy and numeracy are strongly related across development, but the mechanisms underlying their association remain debated. In this study, we adopted a mutualism-based framework, focusing on longitudinal couplings between cognitive and/or academic domains including word reading, mathematics, and various cognitive skills in 205 Dutch children followed across five waves from kindergarten (mean age: 5.43 years) to Grade 2 (mean age: 7.41 years). Ten domains were assessed, including phonological skills, vocabulary, symbolic comparisons, applied math, verbal and visuospatial working memory, fluid reasoning, RAN, word reading fluency, and arithmetic fluency. Growth curve analyses revealed that higher initial skill levels in several domains, including phonological skills and RAN, were associated with steeper growth rates in word reading and arithmetic. Moreover, we found positive associations between growth rates across various domains, providing partial support for what we introduce here as the ‘developmental manifold’: the notion that the rate of growth (slope) in one cognitive/academic domain is positively associated with slopes in other domains, across early childhood. Regression analyses further indicated that word reading fluency in Grade 2 was predicted by intercepts (but not slopes) in phonological skills, arithmetic and RAN, beyond the autoregressive effects of prior word reading development. Conversely, arithmetic fluency in Grade 2 was only predicted by autoregressive effects of prior arithmetic. Together, our findings demonstrate the crucial importance of longitudinal, multi-domain measurements to understand the developmental interplay between cognitive/academic domains more commonly studied in isolation.