Doing more than three hours of homework per night may be making younger students sick.

A study conducted by Stanford Graduate School of Education surveyed more than 4,300 students from ten high-performing public and private high schools in affluent California communities, and found that excessive homework causes high stress levels and physical health problems.

‘We found a clear connection between the students’ stress and physical impacts — migraines, ulcers and other stomach problems, sleep deprivation and exhaustion, and weight loss,’ co-author of the study, Denise Pope, told CNN.

Published in the Journal of Experimental Education, the study found that while three hours of homework per night was ‘average’ for these students, there were children doing ‘way more’ – as many as five hours per night.

Fifty-six per cent of the students in the study cited homework as a primary stressor in their lives.

But in privileged schools, where competition among students is fierce and pressure of high academic performance overwhelming, many students describe schoolwork as a dominating force in their lives.

The fact that children growing up in poverty are at-risk for serious disturbances including drug and alcohol abuse, depression and anxiety, is well-supported by research and widely accepted.

But a growing body of research, including Ms Pope’s study, reveals that privileged children may also be at risk thanks to the unrelenting pressure placed on them in school.

Ms Pope said the magic number when it comes to homework is ‘nothing over two hours’ for secondary school and ‘no more than 90 minutes’ for more younger students.