This study focuses on the relationship between students' early academic skills and academic achievement. In this context, it is aimed to examine the predictors of students' early literacy and numeracy skills on their later math and science achievements across countries. A quantitative research approach using a correlational survey design was performed. The sample of this study consists of 15815 fifth-grade students who participated in TIMSS-2019 from Norway, South Africa, and Türkiye. Multiple linear regression analysis was used to analyze data obtained from two different scales and students' math and science tests. The study's findings supported the essential roles that early literacy and numeracy skills play in fifth-grade students' math and science achievement in the three-country contexts. The results revealed that the more frequent involvement of parents in early literacy activities could increase children's later science achievement and that children's ability to perform early numeracy tasks better when beginning primary school could increase students' later mathematics achievement. Another result of the study is that for countries where all of the other early academic skills within the scope of this study are statistically significant, they can contribute positively to students' later mathematics and science achievement, which may be long-term. Finally, it is recommended that activities and tasks to increase parental participation can be included in preschool curricula. In addition, support that can help children develop early academic skills can be provided to children who have not yet started primary school and their parents. [This article includes an extended summary in Turkish.]