The article is dedicated to the memory of Professor of the Department of Medical Psychology and Psychophysiology of the Saint Petersburg State University, a leading specialist in the field of child clinical psychology Irina Ivanovna Mamaychuk. An attempt to analyze and generalize its great scientific and practical contribution to child clinical psychology is made. The stages of her professional path are singled out and described: (1) the study of the mechanisms and types of disturbed development in children with cerebral palsy; (2) study of the psychology of children with various disorders of the musculoskeletal system; (3) empirical substantiation of strategies and technologies for psychological assistance to children with various variants of disturbed development; (4) development of methodological and applied problems of child clinical psychology. The results and conclusions of Irina Ivanovna’s key studies are revealed, which have made a great contribution to understanding the causes and mechanisms of mental disorders in children and adolescents, and embodying the principles of ontogenetic and system-structural approaches developed at the Leningrad — St. Petersburg school of psychology. In particular, the study of the role of motility in perceptogenesis in various variants of dysontogenesis; specifics of violations of interfunctional relationships in children with motor and mental disorders; subspecies of mental retardation of cerebral-organic origin; psychological characteristics of children and adolescents with somatic pathology. Based on the analysis of scientific works, a list of the main problems and prospects of modern child clinical psychology is highlighted. An approach to psychological assistance and psychological correction of disorders in children and adolescents is described, taking into account the role of the family and the immediate environment. It is emphasized that the empirical work of Irina Ivanovna has become the “gold standard” in the study of the problems of children with mental dysontogenesis, and her theoretical generalizations and methodological developments are very important а for the further development of child clinical psychology and understanding the problem of mental development in general.