Students’ mental health has become an increasing concern in high school education in Vietnam, particularly in the context of expanding school-based support activities alongside ongoing policy development. This study examines students’ access to mental health support activities from a school social work perspective, focusing on patterns of engagement, experiences of use, and barriers to implementation. An explanatory sequential mixed-methods design was employed, with quantitative data collected from 310 high school students across 10 schools in Ho Chi Minh City, followed by semi-structured interviews with 22 participants, including students, teachers, and school administrators. The findings indicate that communication activities have the highest level of access, while counselling and referral services remain limited, with a substantial gap between need and access, particularly for more specialized forms of support. No statistically significant differences were found across gender and grade levels, suggesting that these limitations are systemic rather than group-specific. Qualitative results further highlight barriers related to students’ help-seeking behavior, the limited depth of communication activities, and constraints in organizational capacity and coordination. Overall, mental health support activities in schools remain fragmented and insufficiently integrated, and improving their effectiveness requires strengthening system-level coordination, enhancing professional capacity, and developing a coherent support pathway aligned with students’ needs.