The headline
The largest brick-and-mortar US public high schools enroll 4,800 to 5,800+ students. The biggest among them: Brooklyn Technical High School in New York (5,848 students), Conroe High School in Texas (5,252), Carmel High School in Indiana (5,239), Allen High School in Texas (5,206), and Reading Senior High School in Pennsylvania (4,879). These operate at scales typical of small colleges rather than typical high schools.
What "mega high school" actually means operationally
A high school of 5,000+ students typically runs:
- 200-300 full-time teachers
- 50-80 sections of each core course per year
- 20-30 assistant principals and deans
- An athletic department with 50+ teams across all sports and divisions
- Cafeteria operations on multiple lunch shifts to fit the building's seating capacity
The administrative complexity is closer to a small university than a typical American high school.
The research on scale
Whether large high schools serve students better or worse than smaller schools is contested. Some research suggests negative effects of very large enrollments on graduation rates and student belonging; other research finds that large schools can offer course breadth and specialized programs that small schools cannot.
The clearest finding in the research: large high schools tend to be most effective when they organize into smaller learning communities (academies, houses, small learning communities) within the larger structure. Mega-schools that operate as single undifferentiated units tend to underperform their potential.
Why these specific schools are large
The reasons differ by school. Brooklyn Tech is a specialized exam high school drawing from across New York City. Conroe HS and Allen HS serve fast-growing Texas suburban districts that built single comprehensive high schools rather than splitting. Carmel HS serves a wealthy Indianapolis suburb on the same model. Reading SHS serves a high-poverty urban Pennsylvania district that consolidated multiple smaller high schools.
Methodology
Source: NCES Common Core of Data 2024-25. Filter limited to schools classified as High (grades 9-12 or similar) that are not virtual (they deliver instruction in person rather than fully online). Some entries on the list are blended-learning programs that may not meet a strict definition of brick-and-mortar; flagged where applicable.