Homelessness threatens the well-being of over 1.3 million school children in the United States. Many more students are believed to experience homelessness each year, but they go unrecognized. This report provides new estimates of student homelessness in high school, and the experiencing accompanying it, based on data from the 2019 Youth Risk Behavior Surveillance System (YRBSS) across 24 states and 12 school districts. Evidence shows that most student homelessness goes unrecognized: (1) About 509,025 students experienced homelessness across 24 states, approximately 9.17% of all public high school students in these states. State education agencies did not identify at least two-thirds of students who experienced homelessness; (2) About 56,848 students in 12 school districts reported homelessness, approximately 13.68% of all public high school students in these districts. These districts did not identify approximately 29% of homeless students. Findings also show that homelessness rates differ by race, sex, and LGBT identification: (1) Black/African American, Hispanic/Latinx, and Native American/Hawaiian/Alaskan students were more likely to report homelessness than White or Asian American peers; (2) Male students were more likely to report homelessness than female students; and (3) Lesbian, gay, bisexual, or transgender (LGBT) students were more likely to report homelessness. Additionally, students reporting homelessness have higher rates of victimization. According to YRBSS state data, students who reported homelessness had: (1) 315% greater odds of being sexually victimized; (2) 363% greater odds of being physically victimized; and (3) 128% greater odds of being bullied. According to YRBSS school districts data, students who reported homelessness had: (1) 196% greater odds of being sexually victimized; (2) 296% greater odds of being physically victimized; and (3) 128% greater odds of being bullied. Key findings also show that student homelessness accompanies other problems, even when controlling for other risk. According to YRBSS state data, students who reported homelessness had: (1) 132% greater odds of suicidality; (2) 184% greater odds of substance use; (3) 89% greater odds of alcohol abuse; (4) 152% greater odds of risky sexual behavior; and (5) 126% greater odds of poor grades in school. According to YRBSS school districts data, students who reported homelessness had: (1) 111% greater odds of suicidality; (2) 239% greater odds of substance use; (3) 134% greater odds of alcohol abuse; (4) 87% greater odds of risky sexual behavior; and (5) 134% greater odds of poor grades in school. Student homelessness is prevalent in United States high schools, threatens optimal outcomes, and goes unrecognized most of the time. Students and families experiencing homelessness need: (1) well-resourced efforts to prevent housing disruptions and quickly identify, respond to, and resolve homelessness when it occurs; (2) support through coordinated and comprehensive education, health, and human service systems; and (3) robust data systems to oversee efforts while also testing and developing new innovations. [This report was published by Nemours Children's Health System. Abstract modified to meet ERIC guidelines.]