Background: Bullying remains a significant concern in high schools, while supportive teacher-student relationships may contribute to a safer school environment. However, quantitative evidence examining positive teacher communication and teachers’ understanding of bullying prevention strategies together in relation to teacher-student relationships remains limited. This study examined the associations of these two factors with teacher-student social relationship quality among high school students. Methods: This cross-sectional observational study followed the STROBE reporting guideline and included 261 students from a population of 748 students in grades 10–12 selected through stratified random sampling. Data were collected using a 1–5 Likert-scale questionnaire assessing positive teacher communication, understanding of bullying prevention strategies, and teacher-student social relationship quality; validity was assessed using Pearson’s correlation and reliability using Cronbach’s alpha in a pilot study of 20 students from another school. Supplementary semi-structured interviews with seven teachers and guidance counsellors explored communication practices and challenges in addressing bullying. Quantitative data were analyzed using Pearson’s correlation and multiple linear regression at a significance level of 0.05, while interview data were analyzed thematically. Results: Among 261 students, mean scores were 4.2 for positive teacher communication, 4.1 for understanding of bullying prevention strategies, and 4.3 for teacher-student social relationship quality. Positive teacher communication was positively correlated with relationship quality (r = 0.68; p < 0.05), as was understanding of bullying prevention strategies (r = 0.82; p < 0.05). Together, the two predictors explained 79% of the observed variance in relationship quality (R² = 0.79; p < 0.05). Conclusion: Positive teacher communication and teachers’ understanding of bullying prevention strategies were significantly associated with teacher-student social relationship quality. The findings indicate that both factors warrant consideration in school-based approaches to strengthening supportive teacher-student interactions and bullying prevention.