Socio-economic status (SES) has been consistently shown to influence students' educational achievement, but to date, few studies have investigated the role of SES in language learning motivation. This study aims to examine to what extent two indicators of SES, school location and parents' education, affect motivation of Polish 15-year-olds to study English. The questionnaire, completed by 599 participants, was based on Motivational Systems Theory [Ford, M. 1992. "Motivating humans: goals, emotions, and personal agency beliefs." London: Sage Publications.] The results indicate that both school location and parents' education affect language learning motivation. Students from rural schools and those whose parents have a lower level of education tended to be less motivated than their peers from cities and those whose parents have higher levels of education. The differences concerned the goals the students adopted, their personal agency beliefs, emotional arousal processes, ideal L2 selves and self-regulation. This study highlights the need to raise teachers' awareness of the issue. From the methodological perspective, it stresses the necessity to ensure sample representativeness in terms of students' SES when conducting research on affective factors in language learning and calls for more research involving participants from lower SES backgrounds.