To assess the effect of an online comprehensive sexuality education (CSE) package for vocational high school students in China's developed and less-developed regions, a parallel, unblinded, cluster, randomized controlled trial was conducted. The study included 3,415 tenth-grade students from 29 mixed-gender vocational high schools who had not previously received CSE. The intervention group participated in weekly classes over two months, totaling 360 minutes of online CSE. For the primary outcomes, the intervention group exhibited improvements in sexuality knowledge and attitude post-intervention and one year later. However, after one year, the positive effects were less than post-intervention. In addition, the intervention group's growth rate of sexuality knowledge and attitude was not limited by the initial baseline level. In the secondary outcomes, compared with the control group, the online CSE resulted in a higher frequency of penetrative sexual events, harassment coping self-efficacy in both post-intervention and one year later, and school bully perception only in post-intervention. No significant between-group differences were observed in the trajectory of STD symptom changes, contraceptive usage, unintended pregnancy rates, or self-efficacy. Finally, curriculum progress positively impacted the slope of sexuality knowledge and attitude. Results suggest that more sustained CSE is necessary for vocational high school students in China. Online CSE presents a feasible solution to enhance sexuality knowledge and attitude and bridge the gap in developmental and sexuality education levels. However, behaviors and well-being outcomes did not yield consistent positive results.
