Students’ mathematics achievement is shaped by a combination of internal and external factors, with family support potentially playing an important role in boarding school contexts. This study investigates the factors associated with mathematics achievement among Grade VIII students and addresses the question of whether internal and external factors, particularly family-related factors, are associated with differences in achievement. A quantitative survey design was employed with 48 Grade VIII students from Muhammadiyah Boarding School Palopo, Indonesia, comprising 24 students from Grade VIII A and 24 from Grade VIII B. Data were collected through a validated and reliable questionnaire measuring internal and external factors and students’ mathematics achievement, and were analyzed using ordinal logistic regression. The results indicate that no individual factor reached statistical significance at the 5% level. Nevertheless, parental upbringing and parental support demonstrated the strongest potential associations with mathematics achievement, with significance values of 0.072 and 0.108, respectively. The model explained 22.5% of the variation in students’ mathematics achievement, while 77.5% was attributable to factors outside the model. These findings suggest that family support may be more relevant than school-related factors in understanding mathematics achievement, highlighting the importance of strengthening parental engagement and home-based learning support while encouraging further research into the other factors that explain students’ achievement.