Project Cal-Well is a cross-agency mental health initiative led by the California Department of Education focused on building capacity for sustainable school-based mental health systems in local educational agencies (LEAs) throughout California. As part of a series highlighting the work of Project Cal-Well partners in Cohort 2 (2019-2024), this brief summarizes how Northern Humboldt Union High School District leveraged Project Cal-Well funding to shift to a Multi-Tiered System of Support approach to implement a sustainable school mental health system, strengthen connections with community partners, and empower staff to take a proactive approach to supporting students' mental health.