Class size statistics show how many students teachers typically serve in a class, but the answer depends on the school level, teaching arrangement, school sector, and measurement method. In 2020-21, U.S. public-school averages ranged from 16.9 students in self-contained middle-school classes to 22.0 in departmentalized middle-school classes. The same year, private-school averages were generally lower, while OECD data put average class size at 21 students in primary education and 23 in lower-secondary education in 2022 (school year 2021/22).
Contents
- How U.S. class-size measures differ
- Public-school averages by level and instruction
- Traditional public and charter schools
- Private-school class sizes
- Pupil-teacher ratios over time
- Ratios by public-school enrollment
- International benchmarks
How U.S. class-size measures differ
The National Center for Education Statistics (NCES) reports 2020-21 class-size estimates as weighted averages reported by teachers. The tables distinguish self-contained instruction, in which one teacher generally teaches the class across subjects, from departmentalized instruction, in which students move among teachers or subjects. These are class-size estimates, not a count of every student assigned to a school.
NCES also reports a separate pupil/teacher ratio. That ratio includes special-education and other special teachers generally excluded from classroom class-size calculations, so it should not be read as a classroom headcount. The ratio is useful for staffing context, while the class-size tables are more directly suited to describing the number of students in a reported class.
The figures below retain their measurement periods. The U.S. class-size tables refer to 2020-21, the NCES ratio series refers to fall 2010 through fall 2021, and the OECD reference year 2022 means the 2021/22 school year.
Public-school averages by level and instruction
In public schools during 2020-21, departmentalized classes were larger than self-contained classes at the elementary, middle-school, and secondary/high-school levels. Elementary self-contained classes averaged 19.1 students, compared with 20.7 students for departmentalized instruction. Middle-school classes averaged 16.9 students when self-contained and 22.0 when departmentalized. At the secondary/high-school level, the corresponding averages were 17.2 and 21.0 students.
Public combined/other-grade schools showed a smaller gap between the two arrangements. Self-contained classes averaged 17.1 students, while departmentalized classes averaged 17.9 students. This distinction matters when comparing a reported school average with an individual teacher’s schedule: the same school level can contain materially different class structures.
| Public-school level | Self-contained | Departmentalized |
|---|---|---|
| Elementary | 19.1 | 20.7 |
| Middle school | 16.9 | 22.0 |
| Secondary/high school | 17.2 | 21.0 |
| Combined/other grade | 17.1 | 17.9 |
Source: NCES, Average public school class size, 2020-21.
The public-school figures describe averages, so they do not indicate that every class had the same enrollment. They also should not be used to calculate a school’s pupil-teacher ratio: NCES identifies those as different measures with different inclusions.
Traditional public and charter schools
Traditional public and charter schools had notably different reported patterns in several 2020-21 categories. In traditional public schools, elementary self-contained classes averaged 19.0 students and departmentalized classes averaged 20.5. Traditional public middle-school averages were 16.6 and 22.0, respectively. At the secondary/high-school level, traditional public self-contained classes averaged 16.1 students and departmentalized classes averaged 21.0.
The charter-school estimates were higher in the reported self-contained categories. Charter elementary self-contained classes averaged 20.8 students, while departmentalized classes averaged 22.4. Charter middle-school self-contained classes averaged 26.2 students and departmentalized classes averaged 22.2. Charter secondary/high-school self-contained classes averaged 27.5 students, compared with 20.2 for departmentalized instruction. In charter combined/other-grade schools, the averages were 24.1 students for self-contained classes and 21.3 for departmentalized classes.
| School type and level | Self-contained | Departmentalized |
|---|---|---|
| Traditional public elementary | 19.0 | 20.5 |
| Traditional public middle | 16.6 | 22.0 |
| Traditional public secondary/high | 16.1 | 21.0 |
| Charter elementary | 20.8 | 22.4 |
| Charter middle | 26.2 | 22.2 |
| Charter secondary/high | 27.5 | 20.2 |
Source: NCES, Average public school class size, 2020-21.
These comparisons are descriptive. The reported averages do not by themselves explain why charter and traditional public figures differ, and the variation between self-contained and departmentalized instruction means that school type alone is not enough to interpret a class-size number.
Private-school class sizes
Private-school averages in 2020-21 were 14.2 students for all private elementary/middle-school self-contained classes and 14.5 for departmentalized classes. For all private secondary/high schools, self-contained classes averaged 16.1 students and departmentalized classes averaged 15.8. Combined/other-grade private schools reported averages of 14.8 students in self-contained classes and 14.5 in departmentalized classes.
| All private schools | Self-contained | Departmentalized |
|---|---|---|
| Elementary/middle | 14.2 | 14.5 |
| Secondary/high | 16.1 | 15.8 |
| Combined/other grade | 14.8 | 14.5 |
Catholic private schools showed a different pattern by level and teaching arrangement. Catholic elementary/middle-school classes averaged 17.4 students in self-contained instruction and 17.9 in departmentalized instruction. Catholic secondary/high-school self-contained classes averaged 33.5 students, while departmentalized classes averaged 19.0. Catholic combined/other-grade schools averaged 17.9 students in self-contained classes and 18.0 in departmentalized classes.
The 33.5-student Catholic secondary/high-school self-contained estimate is substantially higher than the all-private secondary/high-school self-contained average of 16.1. It is best read as a category-specific average, not as a general description of private schools. The private-school source also separates affiliation, which is why “all private” and “Catholic private” figures should not be treated as interchangeable.
Source: NCES, Average private school class size, 2020-21.
Pupil-teacher ratios over time
The NCES public-school pupil/teacher ratio declined from 16.4 pupils per teacher in fall 2010 to 15.4 in fall 2021. The annual values were 16.3 in fall 2011, 16.4 in fall 2012, 16.3 in fall 2013, 16.2 in fall 2014, 16.2 in fall 2015, 16.2 in fall 2016, 16.1 in fall 2017, 16.1 in fall 2018, 15.9 in fall 2019, 15.5 in fall 2020, and 15.4 in fall 2021.
| Fall | Pupils per teacher | Fall | Pupils per teacher |
|---|---|---|---|
| 2010 | 16.4 | 2016 | 16.2 |
| 2011 | 16.3 | 2017 | 16.1 |
| 2012 | 16.4 | 2018 | 16.1 |
| 2013 | 16.3 | 2019 | 15.9 |
| 2014 | 16.2 | 2020 | 15.5 |
| 2015 | 16.2 | 2021 | 15.4 |
Source: NCES Digest, Public elementary and secondary pupil/teacher ratios, fall 2010 through fall 2021.
This series is a staffing ratio rather than a direct trend in the size of every classroom. Because special-education and other special teachers are generally included in the pupil/teacher calculation but excluded from class-size calculations, the two measures can move differently.
Ratios by public-school enrollment
In fall 2021, public schools enrolling fewer than 300 students had a pupil/teacher ratio of 12.1. Schools enrolling 300 to 499 students had a ratio of 14.3, while schools enrolling 500 to 999 students had a ratio of 15.6.
| Public-school enrollment | Pupils per teacher, fall 2021 |
|---|---|
| Under 300 students | 12.1 |
| 300–499 students | 14.3 |
| 500–999 students | 15.6 |
Source: NCES Digest, Public elementary and secondary pupil/teacher ratios, fall 2010 through fall 2021.
The available enrollment categories show a lower ratio in smaller public schools than in the two larger categories listed here. This remains a pupil/teacher comparison, not a claim that each class in a smaller school contained 12.1 students or that each class in a 500-to-999-student school contained 15.6.
International benchmarks
OECD data provide a broader benchmark for 2022, covering the 2021/22 school year. Average class size was 21 students in primary education and 23 students in lower-secondary education. Across OECD countries with available data, primary classes were below 25 students in every country except Chile, Israel, Japan, and the United Kingdom.
The OECD averages also distinguish public and private institutions. Average primary class size was 21 students in public institutions and about 20 in private institutions. At lower-secondary level, the averages were 23 students in public institutions and 21 in private institutions.
| OECD 2022 level | Public institutions | Private institutions | Overall OECD average |
|---|---|---|---|
| Primary | 21 | About 20 | 21 |
| Lower-secondary | 23 | 21 | 23 |
Source: OECD, Education at a Glance 2024.
The OECD definition is narrower than a general school staffing ratio: it describes students following a common course and excludes special-needs programs and subgroup teaching. It is therefore a useful international class-size benchmark, but it should not be combined mechanically with NCES pupil/teacher ratios.
The international trend was mixed in the supplied comparisons. Korea’s average lower-secondary class size fell by 7 students between 2013 and 2022, while the United Kingdom’s increased by 4 students over the same period. Those are changes across the stated 2013-2022 period, not forecasts, and they do not establish a universal direction for class sizes across OECD countries.