High school supplementary enrollment refers to the process of admitting students into a high school beyond the regular admissions criteria. This additional enrollment is often used to fill remaining spots in a school's student body or to provide educational opportunities to students who may not have met the standard admissions requirements.

The practice of supplementary enrollment is becoming increasingly common in the United States due to various factors. One primary reason is the competitive nature of high school admissions, where many schools have limited capacity and high demand. According to a report by the National Center for Education Statistics (NCES), in the 2019-2020 school year, approximately 84% of public high schools had open enrollment policies, but only 46% of these schools had no waiting lists. This indicates a significant number of schools are utilizing supplementary enrollment to manage their student populations effectively.

Another reason for the rise in supplementary enrollment is the emphasis on diversity and inclusion in education. Schools often use supplementary enrollment to ensure a diverse student body, which can lead to a richer educational experience for all students. For instance, the Los Angeles Unified School District (LAUSD) has implemented a policy that allows students to attend any school within the district, regardless of their neighborhood, as long as there is space available. This policy has been successful in promoting diversity and reducing racial segregation in schools.

Data from the NCES also reveals that supplementary enrollment can have a positive impact on student outcomes. A study published in the "Journal of Education for Students Placed at Risk" found that students admitted through supplementary enrollment were more likely to graduate from high school and attend college compared to those who were not admitted through this process. This suggests that supplementary enrollment can provide educational opportunities to students who may have otherwise been underserved.

In conclusion, high school supplementary enrollment is a crucial mechanism for managing student populations and promoting diversity in education. It allows schools to provide educational opportunities to a broader range of students and can lead to improved outcomes for those who participate. The increasing use of supplementary enrollment in the United States reflects the evolving landscape of high school education and the importance of ensuring that all students have access to quality education.