Summary Subclinical psychotic symptoms are a pluripotent transdiagnostic risk factor, associated both with an increased risk of subsequently developing a serious mental illness (psychotic or non) and current psychiatric distress. However, attempts to prevent the onset of these chronic illnesses in individuals with subclinical psychotic symptoms have had limited success. This may be due to the majority of prior studies focusing on a relatively late stage of risk, when the illness processes are possibly well underway and thus more difficult to reverse. Intervening earlier in the lifespan, during adolescence - a time characterized by high levels of neuroplasticity - could be particularly important for preventive interventions, while also addressing the highly pressing current need for more mental health services for youth. During the past few years, we have developed and tested a brief, group-based intervention for young adults, called Resilience Training (RT). RT focuses on increasing capacities that support social functioning, including social cognition, the neuropsychological processes involved in accurately perceiving others and their mental states. When these capacities are enhanced, such improvements may lead to lower rates of psychopathology. In two published trials, we have reported that RT led to reductions in a range of symptoms and improved social functioning. Additionally, improvements in social cognition, particularly in Theory of Mind, the ability to understand the mental states of others, are linked to RT-related decreases in psychiatric symptoms and improvements in social functioning in this at-risk young adult group. Based on these prior findings, the goal of the proposed project is to adapt RT for at-risk adolescents who will be recruited using a brief mental health screening administered in their high schools, which will identify those who have subclinical psychotic symptoms but are not yet receiving any mental health treatment. We will first test the adapted intervention for its feasibility and acceptability in this population, and then conduct a pilot randomized, waitlist-controlled trial, to test for its efficacy in reducing transdiagnostic symptoms and improving social functioning. We will also measure whether the proposed target mechanism of the intervention, social cognition, plays a role in any intervention-related improvements. If the hypotheses of this project are confirmed, it will be followed by a definitive, longitudinal, randomized control trial, which will measure the efficacy of this novel intervention for preventing disability in transdiagnostically at-risk adolescents. During the course of this project, with the guidance of a highly experienced multi-disciplinary mentorship team, coursework, and a comprehensive training plan that involves training in research on social cognition, adolescent mental health, longitudinal biostatistics, and intervention adaptation, the applicant will develop the necessary knowledg...