The purpose of this study is to evaluate if a trauma treatment called Trauma Systems Therapy (TST) decreases children's mental health symptoms (such as acting out, not controlling their emotions, etc.) as a result of a traumatic event (or events). A traumatic event or events can include experiencing or witnessing violence, excessive bullying, war, car accident, serious injury, getting mistreated or anything else that makes one feel scared or frightened. Children/teens who experience traumatic events have been shown to be at higher risk of poor mental and physical health. Trauma can impact family life, school life and interpersonal relationships well into adulthood. Unfortunately, most children who have experienced traumatic events do not undergo treatment. Although promising treatments do exist, most do not address the complexity of trauma, particularly related to ongoing stress and threats to safety in their environments. One hundred and twenty eligible youth will be randomized to receive either treatment with TST at NYU's Child Study Center or trauma treatment as usual (TAU) at a community mental health clinic.