Every year, an increasing number of autistic youth enter a complex and underfunded adult service system after graduating from high school. Executive function (EF) challenges commonly co-occur with autism, especially related to flexible problem-solving and planning, and are linked to poor outcomes in post-secondary education and employment. The educational system is the primary service access point for autistic youth; however, evidence-based practices are rarely used to support them, and none exist to support pivotal EF skills in transition-age autistic youth. To meet this need, we developed "Unstuck & On Target: Ages 14-22," a school-based curriculum designed to increase independent, flexible problem-solving, planning, and self-advocacy skills in transition-age youth. We describe the iterative development of the "Unstuck: 14-22" curriculum and present implementation outcomes from a school-based trial. Ten schools, from which we enrolled 55 autistic 9th-12th graders with IQ [greater than or equal to] 80 were randomized to treatment as usual (TAU) or "Unstuck: 14-22" delivered by school staff. Teachers taught 25 lessons over a school year and provided implementation-related feedback on each lesson, which we used to revise curriculum content and materials. All "Unstuck: 14-22" schools taught the curriculum in its entirety, and teachers delivered it with high fidelity. Feasibility, acceptability, and satisfaction were similarly high. Findings indicate that "Unstuck: 14-22" could help build educators' capacity to provide targeted treatment to autistic youth in schools, which could be more widely accessed than clinic-based care. Trial registration NCT03199937, https://clinicaltrials.gov