Indicator D2. What is the student-teacher ratio and how big are classes?

The indicator on class size is limited to primary and lower secondary education. At higher levels of education, class sizes are difficult to define and compare, as students are often split into several different classes at these levels, depending on the subject matter.

At the primary level, the average class in OECD countries is 21 pupils. There are fewer than 28 pupils per class in nearly all of the countries with available data, with the exception of Chile with 31 pupils (Table D2.1).

At lower secondary level, average class size in OECD countries is 23 students. Among all countries with available data, it varies from fewer than 20 students per class in Estonia, Finland, Latvia, Lithuania, Poland and the Russian Federation to more than 30 students per class in Costa Rica and Japan (Table D2.1).

The number of students per class tends to increase between primary and lower secondary education. In Costa Rica, it increases by 17 students. On the other hand, in the United Kingdom and, to a lesser extent Australia, Chile, Hungary and the Russian Federation, the number of students per class decreases between these two levels of education (Table D2.1).

Class size is one factor that parents may consider when choosing a school for their children. Hence, the difference in average class size between public and private schools (and between different types of private institutions) could influence enrolment.

In most OECD countries, average class sizes do not differ between public and private institutions by more than one student per class at both primary and lower secondary level. However, in some countries (including Colombia, the Czech Republic, Latvia, Poland, the Russian Federation and Turkey), the average class in public primary schools has at least six students more than the average class in private schools (Table D2.1) . However, with the exception of Brazil and Colombia, the private sector is relatively small in all of these countries, representing at most 5% of students at primary level (Education at a Glance Database). In contrast, in Chile, Greece, Korea and Spain the average class in private institutions is bigger than in public institutions by at least three students.

At lower secondary level, where private institutions are more prevalent, the comparison of class size between public and private institutions shows a more mixed picture. The average class in private lower secondary institutions is larger than in public institutions in 9 countries, smaller in 18 countries and the same in 6 countries. The differences, however, tend to be smaller than in primary education (Table D2.1).

Between 2013 and 2019, class sizes remained constant at primary level and lower secondary level on average across OECD countries, but this average masks considerably substantial changes in individual countries. At primary level, class size decreased by three students in Brazil and increased by four students in Mexico, over the same period across countries with available data. At lower secondary level, the change is even more striking, where the average class size fell by seven students in Korea and increased by four in the United Kingdom between 2013 and 2019 (Table D2.1).

On average across OECD countries, class size remained constant in both public and private lower secondary institutions between 2013 and 2019 (Figure D2.1). This average masks more substantial changes in individual countries: in Estonia, for example, the average class sizes in both public and private institutions were among the lowest in 2013 and remained below the OECD average in 2019, despite an increase over the period. Interestingly, other countries such as Korea, with the highest average class size in 2013, experienced a decrease in class size between 2013 and 2019, both for public and private institutions (Table D2.1).

The ratio of students to teaching staff compares the number of students (full-time equivalent) to the number of teachers (full time equivalent) at a given level of education and in similar types of institutions. It does not consider the amount of instruction time for students compared to the length of a teacher’s working day, nor how much time teachers spend teaching.

At primary level, there are 15 students for every teacher on average across OECD countries. In OECD and partner countries, the student-teacher ratio ranges from 9 to 1 in Greece and Luxembourg to over 23 to 1 in Brazil, India, Mexico and the Russian Federation. Student teacher ratios vary even more at lower secondary level, from fewer than 10 students per teacher in Austria, Belgium, Finland, Greece, Latvia, and Portugal to more than 25 students per teacher in Colombia and Mexico (Figure D2.1).

On average, there are fewer students per teacher at secondary level (13) than at primary level (15) (Table D2.1). The lower student-teacher ratio at secondary level may result from higher instruction time (as instruction hours tend to increase with the education level, so does the number of teachers) or from lower teaching hours (teaching time decreases with the level of education as teacher specialisation increases).

At upper secondary level, the OECD average is about 13 students per teacher and the difference between general and vocational programmes in student-teacher ratios varies across countries. On average, the ratio of students to teaching staff in upper secondary vocational programmes and that in upper secondary general programmes are the same (13 to 1 in both types of programmes) (Table D2.1). While the difference between the two is negligible in a few countries, there are, in fact, around as many countries where the ratio is greater in vocational programmes as there are countries where it is lower. In Latvia, vocational programmes (18 to 1) have twice as many students per teacher as general programmes (9 to 1). This may be due to the fact that in some countries, vocational programmes are significantly work-based, thus vocational students spend considerable time outside of school. As a result, schools need fewer teachers, which may translate into higher student teacher ratios (OECD, 2017[9]). In other countries such as Brazil,, the opposite is true: there are 13 students per teacher in vocational programmes and 25 students per teacher in general programmes, the largest difference among all countries with available data. Depending on the field of study selected, students in vocational education may require more instructor attention, especially as they have access to more sophisticated equipment. In fact, vocational students require more careful supervision as skill specificity rises. This may have important implications in terms of the cost of vocational instruction, as advanced vocational training requires both specialised machinery and a greater level of human resources (Astor, Guerra and Van Acker, 2010[10]).

Although tertiary education may involve more self-learning than primary and secondary education, the number of students per teacher remains an important concern. The student-teacher ratio is considered to be a proxy of quality in education (OECD, 2013[11]). Students are more likely to receive more support and attention when the student-teacher ratio is low (Biddle, 2002[12]). At tertiary level, the student-teacher ratio ranges from 5 to 1 in Luxembourg and 9 to 1 in Norway to over 20 to 1 in Belgium, Brazil, Colombia, India, Ireland and Turkey. In Colombia, the student-teacher ratio in tertiary education reaches 27 to 1 (Table D2.2).

Differences between public and private institutions in student-teacher ratios are similar to those observed for class size. On average across countries for which data are available, the ratio of students to teaching staff is slightly higher in public institutions than in private institutions at lower and upper secondary level (Table D2.3).

At lower secondary level, large differences between public and private institutions are found in Colombia, Mexico and Turkey, where there are at least eight more students per teacher in public institutions than in private ones. In all these countries, however, less than 20% of lower secondary students are enrolled in private institutions (Education at a Glance Database). In contrast, the student-teacher ratio is lower in public institutions than in private institutions in some countries. This difference is most pronounced in Chile, where around 40% of students are enrolled in public institutions (Education at a Glance Database). In this country, the student-teacher ratio is 15 to 1 in public institutions, compared to 23 to 1 in private institutions (Table D2.3).

At upper secondary level, the student-teacher ratio is greater in public institutions than in private institutions in 17 countries, smaller in public institutions in 15 countries, and similar for both sectors in 4 countries. Mexico has the highest difference in student-teacher ratios at this level, with 25 students per teacher in public institutions and only 14 students per teacher in private institutions (Table D2.3). This mixed pattern in upper secondary education may, in part, reflect differences in the types of programmes offered in public and private institutions. For instance, in Norway, few private schools offer vocational programmes, in which the student-teacher ratio is typically lower than the ratio in general programmes (Education at a Glance Database).

There are two categories of instructional personnel (teachers):

  • Teachers’ aides and teaching/research assistants include non-professional personnel or students who support teachers in providing instruction to students.

  • Teaching staff refers to professional personnel directly involved in teaching to students. The classification includes classroom teachers, special education teachers and other teachers who work with a whole class of students in a classroom, in small groups in a resource room, or in one-to-one teaching situations inside or outside a regular class. Teaching staff also include departmental chairs whose duties include some teaching, but exclude non-professional personnel who support teachers in providing instruction to students, such as teachers’ aides and other paraprofessional personnel.

Class size is calculated by dividing the number of students enrolled by the number of classes. In order to ensure comparability among countries, special needs programmes are excluded. Data include only regular programmes at primary and lower secondary levels of education, and exclude teaching in subgroups outside the regular classroom setting.

The ratio of students to teaching staff is obtained by dividing the number of full-time equivalent students at a given level of education by the number of full-time equivalent teachers at that level and in similar types of institutions. At tertiary level, the student-teacher ratio is calculated using data on academic staff instead of teachers.

For the ratio of students to teachers to be meaningful, consistent coverage of personnel and enrolment data are needed. For instance, if teachers in religious schools are not reported in the personnel data, then students in those schools must also be excluded.

For more information, please see the OECD Handbook for Internationally Comparative Education Statistics 2018 (OECD, 2018[13]) and Annex 3 for country-specific notes (

Data refer to the academic year 2018/19 and are based on the UNESCO-UIS/OECD/Eurostat data collection on education statistics administered by the OECD in 2020 (for details, see Annex 3 at:


[10] Astor, R., N. Guerra and R. Van Acker (2010), “How can we improve school safety research?”, Educational Researcher, Vol. 39/1, pp. 69-78,

[12] Biddle, B. (2002), “Small Class Size and Its Effects”.

[2] Bouguen, A., J. Grenet and M. Gurgand (2017), “Does class size influence student achievement?”, IPP Policy Breif, No. 28, Institut des Politiques Publiques, Paris,

[6] Chin, O. (2008), “Students’ questions: a potential resource for teaching and learning science”.

[7] Frijters, S., G. ten Dam and G. Rijlaarsdam (2008), “Effects of dialogic on value-loaded critical thinking”, Learning and Instruction, Vol. 18/1, pp. 66-82,

[5] OECD (2021), The State of School Education: One Year into the COVID Pandemic, OECD Publishing, Paris,

[1] OECD (2020), Education at a Glance 2020: OECD Indicators, OECD Publishing, Paris,

[4] OECD (2019), Working and Learning Together: Rethinking Human Resource Policies for Schools, OECD Reviews of School Resources, OECD Publishing, Paris,

[13] OECD (2018), OECD Handbook for Internationally Comparative Education Statistics 2018: Concepts, Standards, Definitions and Classifications, OECD Publishing, Paris,

[9] OECD (2017), “Bullying”, in PISA 2015 Results (Volume III): Students’ Well-Being, OECD Publishing, Paris,

[3] OECD (2016), PISA 2015 Results (Volume II): Policies and Practices for Successful Schools, OECD Publishing, Paris,

[11] OECD (2013), OECD Skills Outlook 2013: First Results from the Survey of Adult Skills, OECD Publishing, Paris,

[8] Parks-Stamm, E., M. Zafonte and S. Palenque (2016), “The effects of instructor participation and class size on student participation in an online class discussion forum”, British Journal of Educational Technology, Vol. 48/6,

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