Aims and objectives: In Dagestan, Russian is the language of education, urban way of life, and upward social mobility, and the means of communication between speakers of different languages. This is a result of a quick and drastic change. At the end of the 19th century, Russian was spoken by less than 1% of the population. The aim of this paper is to understand how such rapid spread of Russian as an L2 became possible. Approach: The study uses quantitative data on Dagestanians’ language repertoires. We relate the command of Russian to certain facts from people’s biographies, such as the level of education, migration, warfare and military service, and other professional experience, and run regression analysis. Data and analysis: The data were collected by the method of retrospective family interviews during numerous field trips to highland Dagestan. We use information on 3519 individuals collected in 27 villages. Findings/conclusions: We conclude that the compulsory school education introduced in Dagestan in the 1930s is the social mechanism that resulted in the spread of Russian and its later development into a lingua franca. Russian was imposed from above and supported by the ideology that associated it with future and progress. Originality: This is the first attempt to apply quantitative methods to a large collection of field data to reveal social mechanisms underlying the spread of a single L2 instead of local bilingualism. Significance/implications: The spread of one lingua franca across a large territory is attested in many areas. We suppose that lingua francas of different origin result from different constellations of social factors and show that in Dagestan lingua franca was imposed by the authorities via a systematic educational campaign. We also suggest it was the extreme linguistic diversity of Dagestan that brought Russian from a widely known L2 to a lingua franca.