Holliston High School in Holliston, Massachusetts has taken part in a national screening programme, which is believed to be the first time a school has checked such a large number of pupils for signs of depression.

The school's principal, Keith Gerritt, said that an earlier survey had shown that up to 15% of teenagers had contemplated suicide, and the screening would encourage pupils to seek help.

"We're becoming more aware of the extent of the problem of depression," said Mr Gerritt. "This event can raise students' awareness, so that they know the warning signs for themselves and their friends."

"There are now seven, eight and nine year olds who are clinically depressed."

The school's 1,100 pupils were given questionnaires which sought to provide a psychological profile of how they felt about themselves and their future.

Parents were allowed to withdraw pupils from the tests, but a large majority of pupils answered the questionnaire, which was given to the school as part of National Depression Screening Day.

The anonymous test allowed pupils to check their own emotional well-being, with offers of counselling and advice for any students who found that their profile suggested they were at risk.

After the survey, Mr Gerritt said that a number of pupils went to visit the school psychologist.

The overall results will be used by the school to develop strategies to reduce the threat of suicide and depression among pupils.

The national screening day for depression seeks out difficulties such as a persistent sense of "hopelessness" and "worthlessness", changes in appetite, loss of energy and interest, thoughts of suicide, irritability and difficulty in making decisions.