A special psychologist needs to know the unique mental development of a mentally retarded child. Knowledge of the characteristics of mental development will help the psychologist to competently solve the problems of psychological correction and support for students of a special (correctional) school of the VIII type. Seminars and practical classes that develop students' interest in the theory and practice of special psychology, contribute to deepening knowledge in this area. The manual presents the following sections for studying the psychology of mentally retarded children and adolescents - “Systematics of mental retardation conditions”, “Diagnostics of persons with mental retardation” ", "Behavioral disorders in children and adolescents with mental retardation", "Peculiarities of perception in children and adolescents with mental retardation", "Development of mentally retarded children and adolescents", etc. After each chapter, where theoretical material is briefly presented, questions and tasks for independent work, as well as a list of recommended literature. The manual is addressed to students of medical and pedagogical universities, graduate students, speech pathologists and practicing specialists.