Abundant evidence demonstrates that traumatized adolescents are at increased risk for a host of negative psychoeducational and functional outcomes, but demographic disparities are often seen in access to and use of mental health services and supports. In light of this, the current study examines the prevalence of trauma experiences and traumatic stress in middle school students from a large urban school district serving a high proportion of diverse immigrant and low-income families. Descriptive statistics document the mean reported number of trauma experiences and posttraumatic stress subscale scores by participants' sociodemographic variables. Inferential statistics report significant differences associated with race/ethnicity, gender, and type of trauma--including exposure as a victim or a witness. Results show complex and significant racial/ethnic group differences in the experience and symptomatology of trauma among the entire screened sample as well as the subset of youth with elevated distress. Furthermore, findings document the predictive value of particular trauma events related to early adolescents' severity of self-reported traumatic stress. These in-depth findings underscore the need for routine, school-based screening to identify and bring culturally-competent, trauma-informed support and interventions to middle school students experiencing traumatic stress. [This paper was published in "School Mental Health" v8 p89-105 2016 (EJ1229114).]