School-age children are in Piaget’s concrete operational stage. In other words, they can make sense of the physical world and understand how objects behave in space and time. While six-years-olds may still have some trouble with conservation tasks, by age seven most children have a basic understanding of these concepts.

Other cognitive skills are also important. School-age children have a more sophisticated sense of classification. They understand that objects can belong to different categories and that categories can be hierarchically arranged. For example, a child can collect baseball cards of left-handed pitchers or of third basemen in the American League. They can also rearrange these categories, to collect left-handed pitchers in the American League. Their understanding of number, of sequencing, and of spatial relationships also grows. Language also continues to develop and by the end of this stage children have an average vocabulary of 40,000 words.

Because of this ongoing cognitive development, children are ready to learn skills needed for adult life. In industrialized societies, this involves academic skills. Reading, writing, and arithmetic are three academic skills that school-age children have to master in industrialized and economically developed countries.