The paper describes a complex study of the development of cognitive abilities in the process of school ontogenesis. A mass of empirical data obtained in the longitudinal study has enabled the author to establish the typical pattern and temporal regularities in the development of cognitive abilities in schoolchildren, age-related dynamics of the integral index of cognitive abilities and age-related patterns of certain components of cognitive abilities. The data obtained should be borne in mind while planning intellectual and study loads at all stages of school education as well as while carrying out goal-oriented development of cognitive abilities in schoolchildren.