Many working parents worry about sending their kids to daycare: What will the supervision be like? Will my child get along with the other kids? Is it bad for my child? At least one of these stressors is unnecessary, according to a new study on the effects of daycare on child behavior.

Research that tracked almost 1,000 Norwegian children through daycare found that the amount of time children spent in daycare had little effect on aggressive behavior.

“From a public perspective, our findings are important because they should help ease parents’ fears about the potential harms of early non-parental child care,” said Eric Dearing, lead author on the study and a psychological scientist at the Lynch School of Education, Boston College in a press release.

Women began entering the workforce in greater numbers in the 1980s, and many more children went to daycare as a result. Some child development researchers began to report that daycare had harmful influences on a child’s social and emotional adjustment. Debate among researchers sprang up, and parents were left uncertain and worried.

“Three decades of follow-up studies have only further fueled this debate,” Dearing explained. “While some studies indicate that beginning care early in life and attending for long hours leads to high levels of behavior problems, such as elevated aggression, other studies indicate no risk associated with child care.”

Dearing and colleagues thought that the Norwegian child care practices allowed for a unique opportunity to address the controversy empirically.

Most parents in Norway have up to a year of leave, so children rarely begin daycare before they are 9 months old. Children then end up entering child care at different ages depending on when they were born — enrollment for publicly funded childcare begins in August. The researchers used this as a natural randomizer, since the child’s birth month, rather than a parent’s preferences, determined when they would enter daycare.

Trained assistants interviewed the parents of 939 children about the time spent in daycare at different ages: 6 months and 1,2,3, and 4 years old. The daycare teacher also reported on aggressive behaviors including hitting, pushing, and biting.

“One surprising finding was that the longer children were in non-parental care, the smaller the effects on aggression became,” Dearing explained.

At age 2, children who had entered daycare at earlier ages showed slightly elevated levels of aggression than their peers who entered later. These differences, however, diminished over time — regardless of how much time the child had spent in childcare.

“At age 2, there was some evidence of small effects of early, extensive, and continuous care on aggression,” Dearing says. “Yet, by age 4 — when these children had been in child care for 2 additional years — there were no measurable effects of child care in any of our statistical models. This is the opposite of what one would expect if continuous care was risky for young children.”

The researchers, with the evidence that early child care is not associated with aggressive behavior, are turning their attention to the potential positive effects that childcare could have on children’s learning and language development.

Source: Dearing E, Daae Zachrisson H, Naerde A. Age of Entry Into Early Childhood Education and Care as a Predictor of Aggression. Psychological Science. 2015.