The goal of this RCT is to refine and examine the feasibility, acceptability and preliminary impact of a theoretically guided intervention that provides system 'boundary-spanning' services to improve mental health service use and outcomes for low-income, transition-age youth with mental disorders (TAYMD). Through the refinement and testing of this intervention, called Cornerstone, we aim to address mental health challenges as well as the practical obstacles, such as lack of education, housing, and employment, that impede successful transition to adulthood. Cornerstone addresses these challenges by providing a service delivery strategy that spans the transition from the child to the adult system.