Each year, nearly 5 million children in the U.S. are suspended or expelled from school. New research from the University of Arkansas found this type of school discipline can lead to higher rates of depression through adolescence and into early adulthood.

The findings, published in Advances in Life Course Research, provide empirical evidence for previous suggestions by scholars that school suspensions and expulsions can have long-term effects on mental health.

Driven by zero-tolerance policies, school suspensions and expulsion rose by roughly 50% from the 1970s through 2010. Exclusionary discipline, once reserved for violent acts, drug use or possession of weapons, has increasingly been imposed for less serious behaviors.

“It evolved from these very clearly problematic behaviors to more subjective things, like disrespect or defiance,” said first author Alexia Angton, assistant professor of sociology and criminology at the University of Arkansas.

In the U.S., six out of 10 schools still use exclusionary discipline, even though researchers have questioned its effectiveness. Boys, economically disadvantaged young people and Black, Latino and Native American students more often receive suspensions and expulsions.

Using the National Longitudinal Study of Adolescent to Adult Health (Add Health), an ongoing study of 20,000 people who were adolescents in the mid-1990s, Angton and her colleagues were able to track how often students who were suspended or expelled reported depression later in life.

Adolescents who were suspended or expelled showed “significantly higher depressive symptoms,” the researchers found. This group’s self-reported rates of depression decreased slightly in their late teens and early 20s, and then rose again as they reached their early 30s, the most recent data available in the Add Health survey.

Scholars have established that early exposure to stress can lead to physical or mental health problems in adulthood. Most of that research, however, has focused on adverse childhood experiences at home, such as physical abuse or substance use by parents.

“We know very little about how these stressors in school shape long-term physical and mental health outcomes. So, this really is an entirely new line of research,” said co-author Michael Niño, U of A associate professor of sociology and criminology and director of the Arkansas Health Equity and Access Lab.

Another study by Niño, published early this year in the journal Socius, showed that students who were suspended or expelled reported poorer physical health from adolescence through middle age.

“Broadly speaking, we definitely need discipline reform,” Angton said. “What can we put into place towards lessening the effects of suspension and expulsion down the line?”

Shauna Morimoto, U of A professor of sociology and criminology and associate dean of the Fulbright College of Arts and Sciences, and Kazumi Tsuchiya, assistant professor of public health at the University of Toronto, were also co-authors on the paper.