HSLS:09 follows a nationally representative cohort of students in ninth grade (roughly ages 14-15) in the United States in the fall of 2009. The study follows them as they progress through high school and transition into postsecondary education and/or the labour force, with a special emphasis on exploring the path that leads students to pursue and persist in science, technology, engineering, and math (STEM) courses, majors, and careers. The base-year study involved a nationally representative sample of 944 public and private high schools. Over 21,000 students responded to the survey, with more information from their parents, school administrators, counsellors, and teachers. The cohort was re-interviewed in 2011, 2012, 2013, and 2016, with post-secondary transcripts linked in 2017-2018 and an additional follow-up planned in 2025.