In the 1870s, Professor Sergey Rachinsky of Moscow University left his botany chair and returned to his ancestral estate of Tatevo in Smolensk province. There, he opened a school for peasant children and served as a teacher, and essentially a father, for nearly thirty years.

The Tatevo school was unlike state-run ones. The children lived in a dormitory, sang in a choir, read in Church Slavonic, drew, and worked in the garden. A particular pride was oral arithmetic: students solved problems in their heads that stumped adults. Around Tatevo, a whole network of schools grew, and their graduates became teachers and priests themselves. Rachinsky's book "The Village School" was read throughout Russia, and his experience was discussed by Tolstoy and Pobedonostsev.

One of the students was Nikolai Bogdanov, the illegitimate son of a peasant woman. Rachinsky noticed the boy's drawings and sent him to the icon-painting workshop of the Trinity-Sergius Lavra. This led to the Moscow School of Painting, Sculpture, and Architecture and Repin's workshop at the Academy of Arts. The artist added "Belsky" to his surname in memory of his native Belsky district.

He repaid his teacher with a painting. In the canvas "Oral Arithmetic. In the Folk School of S. A. Rachinsky" (1895), peasant boys struggle with a problem at the blackboard, while Rachinsky himself stands nearby. The problem on the board is still solved by viewers today: (10² + 11² + 12² + 13² + 14²) / 365. The answer: 2.

After the revolution, Bogdanov-Belsky moved to Latvia and continued to paint village children, now from Latgale. He died in Berlin in 1945, having moved there from Riga in 1944 for treatment. The Tatevo school remained the main theme of his life: in emigration, he painted the Russia he once saw from behind the school desk.