Students' ethnicity and self-concept have been less explored in the Philippine educational setting. Exploring the effects of these factors on the mathematics performance of students who enrolled in classes with diverse ethnicity can provide a better understanding of how to handle this type of educational setup. This study aimed to investigate the relationship between ethnicity, self-concept toward Mathematics, and performance in Math of the Grade 7 students of two boarding schools. A descriptive correlational research design was employed using a survey questionnaire to assess the students' self-concept and the results of the unified institutional test to assess their mathematics performance. The 300 respondents were selected using stratified sampling with their ethnic group as the stratum. The data were treated using descriptive and inferential statistics. The results revealed that the students have moderate self–concept of Mathematics in all ethnic groups. Moreover, findings show no significant relationship between the students' ethnicity and self-concept. However, it revealed a significant relationship between ethnicity and performance in Mathematics and self-concept and performance in Mathematics. Hence, a positive sense of identity and self-efficacy can contribute to the better performance of the students in Mathematics. Moreover, teachers are encouraged to consider the ethnicity of students in delivering instruction in classrooms where students have different ethnic orientations.