Data First

Brought to you by The Center for Public Education

Home > Data Center > What is our average class size?

National Data

According to the National Center for Education Statistic’s Digest of Education Statistics 2012, the national average number of students per teacher was 15.5 in 2010.

Data Source

The National Center for Education Statistics (NCES) calculates the number of students per teacher for the nation as a whole. You can find student per teacher data for specific at the school and district levels at SchoolMatters.


NCES calculates the number of students per teacher using the following formula: Total student enrollment divided by professional instructional staff. NCES  publishes the data annually in their Digest of Education Statistics report.

How to Use the Data

Student-teacher ratios can serve as an estimate of class size, and research has shown that under certain conditions reduced class sizes can boost student achievement. These ratios can also be one measure for judging whether your schools have an adequate supply of teachers.

How the details were measured

The data is presented as the number of students per teacher. It cannot be broken down by race or poverty level.

Limitations of the data

The data defines teachers as all professional school staff members who provide instruction to students, so it does not distinguish between non-core subject-matter teachers (like physical education and art) and core subject-matter teachers (like math and English). Moreover, users should not compare schools and districts across the states, because states submit data with differing definitions.

Key Questions to Ask

What is the average class size?

The average class size is not the same as a student-teacher ratio. The two measures can produce different results, because some teachers may have non-classroom teaching assignments, such as working in a writing center. In order to get a solid grasp of school and district context, you should examine them both in conjunction with one another.

How is the student-teacher ratio calculated locally?

When comparing local rates to state and national ones, you should be sure to know the exact definition of a teacher used within each approach. Student-teacher ratio data collected by NCES uses a fairly broad definition and includes any professional school staff member who provides instruction to pre-kindergarten, kindergarten, or any non-graded classes. Other states and districts may exclude those who teach pre-kindergarten, adult education classes, or non-core subject-matter classes. When comparing local rates to national ones, you should be sure that you are comparing apples to apples and that the data has the same underlying definition of a teacher.

Learn More

Student-teacher ratios can be skewed by certain school and district situations, and you should be sure to examine the data within the local context. For instance, if schools and districts have a large number of part-time teachers, that will make the student-teacher ratio appear higher than it actually is. The size of the school also has a relationship with student-teacher ratios, with smaller schools typically having better ratios and larger schools having worse ones.

One might ask if lowering class size increases student achievement. The common-sense answer is that more teachers will boost achievement since instructors can give students more individualized attention. However, the research presents a more complicated picture, and you should be sure to keep a few things in mind. First, class-size reduction initiatives are expensive, because districts need to hire more teaches and build more classrooms. Moreover, the research appears to show that lowering class size is effective only in certain contexts. While some researchers have not found a strong relationship between smaller classes and higher student achievement, most studies show that when elementary schools make a thoughtful effort to reduce class size, students test scores increase.

The Center for Public Education recently reviewed the literature on class size and student achievement and produced a helpful guide to the issue. The report concludes that “the preponderance of the evidence supports positive effects and academic gains when class size reduction programs in the primary grades are well-designed and properly implemented.”

Additional Resources

Demonstrating success:

Smaller classes benefit Burke County (NC) students—Reducing class size has helped this school district stay on track, even when its student demographic changed with more students speaking English as a second language and more students qualifying for free- and reduced-priced lunch.