How important is class size?

It’s commonly assumed that smaller class sizes are better for students. Small classes allow teachers to give more individualized attention, manage classrooms better, and adapt instruction to students’ needs. But research suggests that the reality is a little more complicated.

The most consistent evidence that smaller class size positively impacts student achievement is at the early elementary school level. The Tennessee STAR experiment found that reducing K-3 classes to between 13 and 17 students boosted achievement, with lasting benefits — especially for low-income and Black students. But when California mandated class size reduction in grades K-3 in 1997, schools needed to hire more teachers and many were forced to hire less experienced teachers, or teachers without full credentials, to meet the demand, which reduced the benefits to students. And the costs of reducing class sizes hampered school districts from funding other educational needs. The bottom line: Small classes alone don’t raise student achievement levels. They need to be paired with effective teaching and appropriate learning activities to make a difference.

At the middle and high school level, small classes seem to have less of an effect on student achievement, suggesting that as students grow more independent, outcomes are shaped more by teacher quality, curriculum rigor, and school resources than by class size alone.

What’s the difference between student-teacher ratio and average class size?

GreatSchools publishes class size information for schools in some states and student-teacher-ratio information in others, depending on what data is available from the Department of Education in each state. It’s important to understand the difference between these two types of data and what they indicate about a school.

When you see class size stats on GreatSchools’ school pages, the number refers to the average class size at the school. Some classes may be larger or smaller than the average number you see. This is especially true in schools that have state-mandated class sizes, which generally affect the lower grades. Schools that have mandated smaller class sizes in grades kindergarten through 3 may have larger class sizes for the upper grades.

Student-teacher ratios are based on the total number of school instructional staff divided by the total enrollment of students. This number may include specialist teachers in the arts, literacy specialists, physical education and special education teachers, who may teach smaller groups of students. As a result, student-teacher ratios may show smaller numbers than the actual average class size.

Student-teacher ratios, which in many states are based upon full-time equivalent (FTE) teachers, can appear high for schools that have a large number of part-time teachers. If, for example, a small school has four part-time teachers, who each work 25% of the time, the student-teacher ratio at this school would be calculated based upon one teacher instead of four (because four teachers at 25% is equal to one full-time teacher). This will make the student-teacher ratio appear higher than it really is. If you think your school data shows an exceptionally high student-teacher ratio, check with your school principal to find out why.

In U.S. public elementary schools, the difference between the student–teacher ratio and the average class size is typically about 10 students. An elementary school with a K–3 student–teacher ratio of 14:1 might, in reality, have an average class size of 24 students. And numbers alone can be misleading. A school may report an average class size of 20 or a student–teacher ratio of 14:1, yet your child could still be placed in a classroom with 30 students.

Looking beyond class size

Class size is just one consideration when you’re evaluating a school for your child. Keep in mind these other factors:

• Teacher quality: Regardless of whether or not your school has small classes, you’ll want to know if the teachers use effective techniques — such as small group work, hands-on activities, individualized instruction — to engage students in learning. Do the teachers work in grade-level teams? Do more experienced teachers mentor the newer teachers? Do the teachers have the opportunity to learn from each other and from experts in their field?
• Student load: This term, particularly relevant in higher grades, refers to the number of students a teacher is responsible for each day. An English teacher who has a student load of 200 may have less bandwidth for assigning and reading papers than a teacher with a student load of 60. Partner teachers/teacher aides/volunteers: Some schools with larger class sizes provide quality instruction by having additional teachers, aides, or parent and community volunteers or in the classroom for part or all of the school day. By effectively using these adults, schools can improve morale for teachers and provide the necessary attention for students. Be aware that these additional adults, who may play a vital role in the classroom, are generally not included in class size and student-teacher ratio statistics. Ask at your school how partner teachers, teacher aides and volunteers are employed in the classroom.
• School size: At the high school level, organizational features linked to size—like closer student — adult ties and manageable teacher loads — are associated with , , and .

What to ask about class size

To learn more about class size and how it relates to student achievement at your school and in your school district, ask questions like these of your school administrators, school site council and local school board.

• How does your school district determine the average class size or student-teacher ratio? Does the number include all staff or just the classroom teachers?
• What’s the difference between the size of your child’s class and the average class size?
• How does the average class size compare to other districts and to the state average?
• Do teachers make an effort to provide individual attention to all students?
• Are there budget cuts planned that will affect on class size at my school?