Medical research is leading American education officials to consider having high school classes start later in the morning. The research says teenagers are more awake later at night than adults are. When teenagers stay up late at night they have problems learning early in the morning.

Researchers in the state of Rhode Island measured the presence of the hormone melatonin in peoples' mouths at different times of the day. Melatonin causes people to feel sleepy.

They found that melatonin levels rise later at night in teenagers than they do in children and adults. And they remain at a higher level in teenagers later in the morning. They say this shows that teenagers have difficulty learning early in the morning. Yet most school systems in the United States begin high school classes at about seven o’clock.

A few school districts have made some changes. In nineteen ninety-six, school officials in Edina, Minnesota changed high school opening from about seven thirty until eight thirty. Two years later, the nearby city of Minneapolis did the same. Teachers there reported that students were no longer sleepy in class and were happier. And staying in school later in the day did not seem to be a problem for students who had jobs after school.

Health experts say teenagers need between eight and nine hours of sleep a night. Students who do not get enough sleep are likely to be late for school, fail to do their homework, fall asleep in class and have trouble taking part in class discussions.

Yet some adults oppose changing school start times. School district officials say it is not possible to carry high school and elementary students on buses at the same time. And parents of young children do not support having elementary schools start earlier in the morning. They say it would require young children to wait for school buses in the dark.

Others do not support a later start time because they say it would limit the time for practicing sports after school. However, the Minnesota schools found that this did not hurt school sports competitions.

More American school districts are discussing the possibility of changing high school start times. Researchers and teenagers say they cannot make the change quickly enough.

This VOA Special English Education Report was written by Nancy Steinbach. Internet users can read and listen to our reports at voaspecialenglish.com. This is Shep O'Neal.