The minister of education, Hirokazu Matsuno, expressed shock at a survey that shows teachers at public elementary and junior high schools are regularly putting in 11-hour days, placing some at risk of dying from overwork.

A survey by the ministry found that the daily workload of teachers has risen by more than 30 minutes on average during a past decade because the number of classes has increased.

The results also serve to underscore the huge contribution that teachers are making to ensure that children get the most out of Japan's education system.

The Ministry of Education, Culture, Sports, Science and Technology carried out the survey last October and November. It looked at 400 public elementary schools and 400 public junior high schools throughout the country.

Principals, vice principals, teachers and full-time lecturers were canvassed for their views, officials said April 28.

Responses were received from 8,951 individuals at elementary schools and 10,687 at junior high schools.

The survey found that teachers at elementary schools worked 11 hours and 15 minutes on average each weekday, up 43 minutes from fiscal 2006. Teachers at junior high schools worked 11 hours and 32 minutes on average, up 32 minutes.

In Japan, the upper limit for overtime working hours to prevent “karoshi,” or death from overwork, is set at 100 hours a month, or an average of 80 hours during a period ranging from two to six months.

If the upper limits are applied to the results of the latest survey, 17 percent of elementary school teachers and 41 percent of junior high school teachers exceeded the threshold of 100 hours in a single month.

In addition, 34 percent of elementary school teachers and 58 percent of junior high school teachers topped the upper limit of 80 hours during a two-to-six month period.

“The survey turned up a serious situation that we cannot overlook,” Matsuno said.

Under revised school curriculum guidelines introduced in 2008, the education ministry increased the number of classes at elementary and junior high schools.

Comparing the results of the latest survey with those of a fiscal 2006 survey, the total hours of “classes” and “preparation for classes” increased by 35 minutes per day in the case of elementary school teachers and 30 minutes for junior high school teachers.

That meant teachers were putting in longer hours.

Individuals in managerial positions also were found to be putting in excessive working hours.

Vice principals at elementary schools worked 12 hours and 12 minutes on weekdays on average, up 49 minutes from fiscal 2006. The corresponding figure for vice principals at junior high schools was 12 hours and 6 minutes, up 21 minutes.

“The tasks that vice principals have to deal with has increased, such as coping with local communities or guardians and releasing school information,” a ministry official said.

It was the first such survey by the ministry since fiscal 2006.

A 36-year-old teacher at an elementary school in Kanagawa Prefecture said he arrives at school around 7:30 a.m. each day. Starting with coaching for morning practice of the track club, he has to give classes, attend staff meetings, prepare for school events and do clerical work. He usually leaves school at 9 p.m., but on busy days takes off at 11 p.m.

“It is difficult for me to continue this working style until the retirement," the teacher said. "It is unavoidable that the workload of teachers has increased in line with changes in society. The problem is that the number of teachers has not increased very much, so the burden has increased on each teacher."