Ongoing education on sexual health and other health promotion topics is critical as young people transition into adulthood. A booster round of education may be an effective strategy to reinforce information previously taught and expand to additional topics relevant later in adolescence. In partnership with a Youth Advisory Council, we co-designed READY, Set, Go!, a booster curriculum for older adolescents with modules covering adult preparation skills, sexual identity, relationships, reproductive health, and mental health. From November 2021 to January 2023, we provided the curriculum to 21 cohorts of 12th grade students (N = 433) in rural communities of Fresno County, CA, and conducted an implementation evaluation to assess its feasibility in school settings, acceptability by participants, and changes in short-term outcomes. Health educators completed implementation logs to track program adaptations. Youth completed pretest/posttest surveys to assess changes in outcomes and participant satisfaction. We used descriptive statistics to examine program adaptations and satisfaction. We used multivariable regression models to examine changes in outcomes, adjusted for sociodemographic characteristics. Health educators completed most activities as planned, with adaptations occurring in response to youth needs and scheduling limitations. Sexual health knowledge, confidence in adult preparation skills, awareness of local sexual and mental health services, and willingness to seek health services all increased significantly from pretest to posttest. Youth feedback was strongly positive. We conclude that booster sexual health education is a promising strategy to address critical knowledge gaps and support health promotion, especially in rural and other under-resourced communities.