Ethnic identification is closely tied to language. Society's appreciation of one's first language and the opportunity to use it may help strengthen ethnic identification. This research examined the relationship between ethnic identifications and school language and investigated other factors that potentially impact language-minority students' ethnic identification. The paper consists of empirical data analysis and follow-up research among Russian-speaking children attending Estonian-language and Russian-language schools in Estonia. The research was based on survey data of 186 students and their parents, utilizing a multiple logistic regression model. School language was overwhelmingly shown to be the most important factor explaining children's ethnic identification. The odds of Russian-speaking children having an Estonian identification were extremely high, over a hundredfold, for children attending Estonian-language schools compared to children attending Russian-language schools. The follow-up study of 8,340 Russian-speaking students and an interview of 224 Russian-speaking students in Estonia confirm the strong relationship of ethnic identification and school language. These are significant findings whose implications need to be considered in policy making and school practices.