The article draws attention to the sphere of historical and pedagogical knowledge. Being a product of the development of human society, it lies at the core of contemporary and future pedagogical culture. The mature conventional wisdom helps people to forge their own path in the modern world, to determine their self-identification and the prospects for their personal growth. The historical heritage of the first half of the 20th century, rich in invariant ideas, scientific and pedagogical experience, is viewed here by means of its inclusion in the construction of all spheres of life in modern Russia and Kazakhstan, including the development of pedagogy and psychology. The article reveals the stages of scientific activity of the outstanding teacher and psychologist A.P. Nechaev, characterizing the main milestones and dynamics of the formation of domestic experimental pedagogy at the beginning of the 20th century. It highlights the scholar’s ideas about syndromic psychology, holistic, mental and moral development of the personality, which are relevant even today. The research is based on conceptual ideas of dialogical pedagogy, problem-personalistic approach, retrospective, comparative historical and historical-phenomenological methods. Experimental pedagogy as a phenomenon of the early 20th century ceased to exist without quite exhausting its capabilities, but it laid the foundation for and determined the strategic development direction of child psychology, pedagogical psychology, genetic psychology, childhood ethnography, differential psychology and differential psychophysiology, and the experiment became a sturdy part of the scholarly apparatus of pedagogy and psychology. The potential of experimental pedagogy made it possible to pose and solve large-scale issues of creating a new school, scientific and pedagogical centers, finding solutions to a wide range of psychological and pedagogical problems, designing research schools that develop natural science, psychological and pedagogical problems of education and upbringing. The invariant ideas of this direction of moral, mental and intellectual development of students are also relevant at the beginning of the 21st century and can be used in the practice of contemporary school education.