Smaller classes are often seen as beneficial, because they allow teachers to focus more on the needs of individual students and reduce the amount of class time needed to deal with disruptions. Yet, while there is some evidence that smaller classes may benefit specific groups of students, such as those from disadvantaged backgrounds, overall evidence of the effect of class size on student performance is mixed.
Class size and student-teacher ratios
Class-size and student-teacher ratios vary strongly as countries weigh the trade-off between recruiting more teachers and investing into other elements of education systems.
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Key messages
The ratio of students to teaching staff depends on how resources for education are allocated. Smaller student-teacher ratios often have to be weighed against measures such as higher salaries for teachers, investment in their professional development, greater investment in teaching technology or more widespread use of assistant teachers, whose salaries are often considerably lower than those of teachers.
Context
Class size varies strongly across countries
On average across OECD countries, there are 15 students for every teacher in primary education and 13 students per teacher in lower secondary education. The average school class in OECD countries has 21 students in primary education and 23 in lower secondary education as the number of teachers per school is generally higher than the number of classes per school. However, there are large differences across countries. In Costa Rica, the average class size at primary level is 16 students, whereas it is 31 students in Chile.
Average class size in primary education, by type of institution (2019)
![Figure: Average class size in primary education, by type of institution (2019)](/adobe/dynamicmedia/deliver/dm-aid--6f259fdc-0d48-42bd-a58e-4c9615bcf084/figure-average-class-size-in-primary-education-2021.jpg?preferwebp=true&quality=80)
Average class size has remained largely unchanged over time
In most countries, average class size changes only slowly. Between 2013 and 2019, the average class size across countries remained constant at lower secondary level both in public and private institutions. However, greater changes can occur within countries as schools are affected by demographic trends at the regional or even local level.
Change in the average class size in lower secondary education, by type of institution (2013 and 2019)
![Figure: Change in the average class size in lower secondary education, by type of institution (2013 and 2019)](/adobe/dynamicmedia/deliver/dm-aid--ebba4d01-e654-4f16-8999-56d6235a381d/figure-change-in-the-average-class-size-in-lower-secondary-education-2013-2019-2021.jpg?preferwebp=true&quality=80)
Related data
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Programmes of work and projects
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The OECD Indicators of Education Systems (INES) programme seeks to gauge the performance of national education systems through internationally comparable data.Learn more
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PISA is the OECD's Programme for International Student Assessment. PISA measures 15-year-olds’ ability to use their reading, mathematics and science knowledge and skills to meet real-life challenges.Learn more
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Meeting the challenges of the 21st Century means that schools must be empowered to play a more central and active role in leading improvements in education. To support this, Schools+ will bring together major education networks to put schools at the centre of education design.Learn more
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TALIS - the Teaching and Learning International Survey - is the world's largest international survey about teachers and school leaders.Learn more
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The Teacher Knowledge Survey (TKS) examines what teachers know about teaching and learning, and how their specialised knowledge of pedagogy relates to their work and training.Learn more