The manual reveals the basic principles and technologies of consultative and diagnostic activities of an educational psychologist, presents its modern methodology, and first of all, the technologies of the stages of assessing the mental development of a child that have been tested by practice. from the formulation of the primary diagnostic hypothesis to the preparation of various types of conclusions based on the results of the assessment. The paper provides a classification of the organization of the diagnostic process, the use of which allows you to optimize the activities of the teacher-psychologist, effectively use the resources available to him. In addition, the manual proposes a system of record keeping, created in reliance on the existing regulatory documents of the Ministry of Education. Addressed to teachers-psychologists of general educational institutions, special (correctional) educational institutions, including PPMS-centers, specialists of PMPK . Can be used by students of pedagogical universities and institutes, psychology faculties, students of advanced training courses for educational workers.