Each year consists of about 6,000 waking hours. Children in America, on average, spend about 1,000 of them in school.

Most American children spend about six hours per day in school—fewer in lower grades and more in higher ones. Over the course of a year, students spend about 1,000 hours in class. How are those hours actually spent? Are they sufficient? Does changing the number of hours make any difference?

Yes, time matters.

Learning takes time. Places where school hours deliver more “time on task” are places where students tend to learn more. This is both obvious and provable: one elegant study found a clever way to verify the educational impact of time school time: it examined the effect of snow days (which vary in number by school and by year) on test results. Sure enough, when snow piles up, scores fall down. A day lost here or there actually does make a measurable difference.

For many students, the Pandemic inflicted the academic equivalent of a year of snow days.

The connection between time in school and learning has been deeply researched. More time focused on learning delivers more learning. The standard school day establishes a minimum baseline for the amount of time when students are supposed to have their brains turned on.

What is a Carnegie Unit?

A Carnegie Unit is 120 instructional hours

What exactly do we mean when we talk about school hours, or a school day, or a school week, or a school year? How much time is enough to add up to a “course”? Definitions like these matter when trying to compare programs.

About a century ago, the Carnegie Foundation played a pivotal role in setting standards for course credit, particularly for higher education. A Carnegie Unit is 120 school hours of instruction. The standard is still in use.

In recent years, critics including the leadership of Carnegie Foundation itself have argued that the standard has "outlived its shelflife" and should be replaced. Why? Because the measure fundamentally implies that "doing time" in a class is valuable, and systems have fossilized around it. Authentic learning should be the measure of educational attainment, not seat time.

International comparisons of school hours are tricky.

In the Ed100 blog
Homework: More time on task

Schools in different parts of the country and around the world use time in varying ways, with different school calendars and seasonal breaks. In an effort to permit comparisons, or at least to spur inquiry, the Organisation for Economic Co-Operation and Development (OECD) collects global data about school hours, most recently in 2023.

Schools in America are comparatively time-intensive, according the OECD data. American kids spend more time in classes than kids in most other countries do.

But the harder you scratch at the data, the harder it is to reach easy insights. The data is gathered by survey, and the methodology and even the questions vary from place to place. Grade level groupings used in the surveys are responsive to the different ways that schools are organized locally, and the surveys are massive.

What counts as school time?

International comparisons of education time are further complicated by the fact that not all learning time fits in the “official” system. In Japan and Korea, for example, formal school days are comparatively short, but there are more of them. Even more importantly, many families in these countries invest significant hours at private after-school and weekend “cram schools” that help their children prepare for standardized tests and college entry exams. Comparing only the official hours of school operation kind of misses the point.

A lot of learning can happen outside of official hours of school operation.

There’s an apples-and-oranges problem, too. Does it make sense to compare school hours spent in systems that are teaching different things? In Japan and China, students spend many hours learning to write characters accurately and legibly, a skill less important in English-speaking countries. The OECD survey suggests that most European countries invest about a tenth of primary-grade school hours in the study of international languages. America doesn't participate in this part of the survey, but the difference is obvious: few American primary schools teach international languages at all.

Comparing the use of time for education is tricky even within the United States. Like many other states, California generally requires 180 days of school per year, including a specified minimum number of total hours for each grade level. Some school districts are shifting to a four-day school week, though this strategy risks harming young students. Some districts conduct school five days per week, but routinely send kids home early to allow for faculty training or meetings.

Amanda Ripley, a noted education researcher and author, focused significant attention on the different ways that schools use time in different countries in her bestseller The Smartest Kids in the World and How They Got That Way.

How much time do students actually spend learning?

The true instructional value of school year is significantly shorter than it seems because not all school hours are instructional hours. A considerable amount of time is consumed by distractions like setting up, moving around, settling in, holding school events, assemblies, testing days, birthday celebrations and the like.

Not all school hours are instructional.

In the Great Recession (~2008-09), many California school districts cut five days from their school calendar. Which five? Not special days like testing days, assemblies, and birthday celebrations — those tend to be preserved. Almost by definition, the days lost were ordinary, unremarkable days with nothing special going on except teaching and learning.

Is instructional time the same for everyone?

In recession conditions, school districts that serve California’s highest-need students generally are more likely to have their school year cut in a recession. Low-income students and students of color are also more likely to lose days of instruction through school suspensions.

Time for relationships

School time is not just about academics. Students learn in connection with other students and with educators. Some charter school operators (like KIPP) regard a longer school day as a vital element of their program design. Beyond the academic effect of additional instructional time, a longer day in school may raise the likelihood that school serves as the central context for children’s social relationships.

This lesson was updated in December 2023.