the principle of the development of higher mental functions in a child at an uneven pace. Different skills, such as language, behavior control, motor ability, and attention, can develop at different rates: some develop faster, others lag behind, creating conflicting patterns of development in the same child. This heterogeneity explains why some developmental disorders, such as hyperactivity or learning difficulties, arise not from a complete lack of ability, but from imbalances and mismatches between different functions. This concept emphasizes the importance of considering the child as a whole, given that each psychological function depends on the development of the others, and that developmental assessments should take into account individual differences in timing and functional integration, rather than focusing solely on obvious delays or deficits.