These studies are again an example of correlation rather than a clear causal relationship, but something that still is very relevant for the guidance on children:

• exposure to suspension and expulsion increases the risk of depressive symptoms in adolescence.
• Age variation in mental health by history of exclusionary discipline from adolescence to adulthood.
• Mental health gap between disciplined and non-disciplined youth slightly dissipates as youth age into early adulthood.
• As individuals begin to transition out of young adulthood, the gap in depressive symptoms widens substantially.

From the press release:

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 were published in the latest issue of Advances in Life Course Research. The study provides 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.

Abstract of the first referenced study:

Exposure to exclusionary discipline has been tied to several deleterious outcomes in adulthood, including contact with the criminal legal system. While this work provides interesting insight into the long-term consequences tied to this form of school punishment, few have attempted to consider whether and how, exclusionary discipline practices, in particular, school suspension and expulsion shape mental health patterning over the life course. Using panel data from the National Longitudinal Study of Adolescent to Adult Health, we contribute to this body of literature by examining whether exposure to school suspension or expulsion shapes depressive symptom trajectories from adolescence to adulthood. Results from our mixed-effects linear growth curve models demonstrate both forms of exclusionary discipline play a significant role in depressive symptom trajectories. We find suspended and expelled youth exhibit significantly higher depressive symptoms in adolescence when compared to their counterparts with no history of suspension or expulsion. Results also show age variation in depressive symptom trajectories by history of exposure to exclusionary discipline. Specifically, results show the depressive symptoms gap between disciplined and non-disciplined youth slightly dissipates as youth age into early adulthood, but as individuals begin to transition out of this stage of the life course, the gap in depressive symptoms widens substantially. Results carry implications for how punitive disciplinary practices in schools shape mental health from adolescence to adulthood.