We tend to take school calendars and timetables for granted – and we think they have no consequences – because they have been handed over to us from previous generations. Yet, from distribution of instruction days across weeks and years to duration and organization of the school day itself, they can have an important impact on the quality and equity of education systems. This blog explores the details.

School years are organized in a variety of ways

The organization of yearly school calendars is directly linked to total intended instruction time for students, often legislated by national or sub-national authorities. Variation across countries is wide: Among middle- and high-income countries, the average number of instruction days per year in primary education ranges from 162 in France to 219 in Israel.

Part of the difference is due to the organization of the school week, which varies, for example, from 4 or 4.5 days in France to 6 days in Israel. Another factor is the total length of school breaks, from less than 9 weeks in Mexico to nearly 18 in Ireland.

There are also differences in the distribution of school breaks through the year as the figure below shows. Although students in Luxembourg and Turkey have 15 weeks of vacation a year, it is split into six breaks in Luxembourg but two in Turkey.

A common pattern is for the longest school break to be at the end of the academic year, often during the summer. The history of this calendar, traditional in Europe and North America and now common across much of the world, is less likely linked to agrarian labour needs, as commonly believed, and more likely associated with a need for standardization as urbanization and income levels increased.

Many countries’ school calendar structure is due more to the influence of colonialism than seasons. The Bangladesh school calendar dates to the British colonial period and is not aligned with local agricultural cycles, requiring students to take exams during the peak wet-season harvest period. Schools in Somalia run from September to June, likely an influence of British and Italian rule, unaligned with the country’s warmer months and with its neighbouring countries, such as Kenya and Uganda. Schools in southern hemisphere territories, such as American Samoa and French Polynesia, follow the northern hemisphere calendar.

School calendars are also influenced by cultural and religious practices. It is common for countries with a Christian background to have institutionalized breaks around Christmas and Easter. In Muslim countries, school calendars may change to adapt to Ramadan. Indigenous schools in Canada, Peru and the United States use ancestral calendars that may take into account moon and seasonal cycles or cultural practices.

Adaptation of school calendars to local contexts can have important equity and learning implications

Using a natural experiment in calendar shifts, a study showed that the overlap between seasonal labour demand and annual school examinations in Bangladesh led to a dropout rate seven percentage points higher for students from agricultural households. In India, the difference was estimated to be from five to seven percentage points. During peak harvest seasons, not only were students from agricultural households more likely to miss class, but also fatigue and injuries from field work hindered exam preparation. School calendars’ lack of resonance with local cultures has contributed to higher teacher absenteeism and lower attendance rates among children from Scheduled Tribes in India.

Some argue school calendars may also influence learning outcomes, especially for poorer students. The idea of the ‘summer slide’, a drop in achievement due to the long period away from classes, has led several schools to adopt year-round education that distributes school days more evenly throughout the year. Insufficient evidence makes it difficult to assess the impact of this change on overall performance, and some have questioned the magnitude of summer learning loss compared with loss distributed across the shorter breaks.

The organization of the school day also matters

Along with the number of school days, their length determines learners’ total instruction time. Again, wide variation exists within and between countries – from an average of fewer than 600 hours of compulsory instruction per year in primary education in Latvia and the Russian Federation to over 1,000 hours in Chile, Costa Rica and Denmark.

More instruction time is broadly associated with better student performance, but the effect tends to be mediated by factors such as instruction quality, classroom environment, school autonomy and accountability. It also depends on what ‘more’ means. Adding a few extra minutes may not make a difference; adding an hour may help; adding three may be counterproductive. In Argentina, lengthening the primary school day reduced the student grade retention by 23%.  If well-used, more instruction time can help foster equity. Across a subset of PISA countries, more instruction time was associated with a greater likelihood of disadvantaged students succeeding academically. More and longer school days are also associated with increased participation of mothers in the labour market.

Over time, there has been a global shift towards providing full-day education. Although double-shifting, where schools take in different groups of students for morning and afternoon sessions, remains common in Latin America and Africa, many countries, including Chile and Ghana, have moved to phase it out or abolish it. In Namibia, the government’s plans to phase out double shifting were hampered by COVID-19, which pushed many reopening schools back to it.

Increasing the length of the school day increases costs. In addition to requiring more school buildings, more teachers and longer work contracts, there may be significant infrastructure implications for existing schools. In Germany, as the country undertook nationwide reform to increase school days’ duration over the past 15 years, many schools had to build cafeterias to be able to provide meals. Those that could not do so were often unable to change their schedules.

Beyond duration, school starting times also matter

A growing body of literature points to benefits from delaying starting times, particularly at the secondary level. In addition to allowing more sleep time, later starts appear to align better with adolescents’ circadian rhythm, with peak alertness in the late morning and evening. A study using students’ random assignments to earlier or later classes in the United States found that delaying the starting time by 50 minutes led to a significant improvement in student performance for all courses, not just the first period. Some studies found even short delays helpful. In Hong Kong, China, a 15-minute delay from 7:45am to 8am was associated with greater attentiveness, fewer behavioural difficulties and better peer relationships between secondary school students. In the United Kingdom, a change from 8:50am to 10am was associated with fewer absences due to illness and improved academic performance.

Finally, recess has also been shown to improve students’ level of physical activity, memory and concentration, as well as their socioemotional development and academic performance. Some countries consider breaks to be part of compulsory instruction time. Denmark and some Spanish regions and autonomous communities regulate recess time by law. Still, as daily recess is often seen as a waste of time, many schools do not offer it. In the United States, in the first five years after the 2001 No Child Left Behind Act, which focused on standardized testing, most districts increased time for tested subjects and 20% of districts decreased recess time by an average of 50 minutes per week.

There is no one model that works, but finding the right model for your country, season and culture matters. Making the wrong decision about when, how long and how many school breaks there should be does make a difference.