Working parents often worry about sending their toddlers to daycare. But the results of a new study that tracked almost 1,000 Norwegian children enrolled in daycare indicate that working parents can breathe a sigh of relief: The amount of time children spent in daycare had little impact on aggressive behavior.

The study is published in Psychological Science, a journal of the Association for Psychological Science.

“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,” says Eric Dearing, lead author on the study and a psychological scientist at the Lynch School of Education, Boston College.

As women entered the workforce in increasing numbers in the 1980s, some child development researchers began reporting that daycare had harmful consequences for children’s social and emotional adjustment. These findings stoked uncertainty and fear among parents, and led to debate amongst researchers in the field.

“Three decades of follow-up studies have only further fueled this debate,” Dearing explains. “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 from the Norwegian Center for Child Behavioral Development, Henrik Daae Zachrisson and Ane Nærde, determined that Norway’s child care practices offered a unique opportunity for empirically addressing this controversy.

In Norway, most parents have up to a year of parent leave, so children in Norway rarely start attending daycare before they are 9 months old. Because publicly funded child care centers begin enrollment in August, children typically enter child care at different ages depending on what time of year they were born. For example, a child born in August would enter daycare at 12 months old, while a child born in February would be 18 months old by the time August enrollment opened.

The researchers were able to use this as a natural randomizer; a child’s birth month, rather than their parents’ preferences, determined what age they started going to daycare.

Trained assistants interviewed parents of 939 children about time spent in daycare at ages 6 months and 1, 2, 3, and 4 years old. Each year, the child’s daycare teacher reported on aggressive behaviors like 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 explains.

When the children were 2 years old, those who had entered at earlier ages displayed modestly higher levels of aggression than peers who entered later. Importantly, these differences in physical aggression diminished over time — regardless of how much time children spent in daycare.

“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.”

“If early, extensive, and continuous non-parental care does, in fact, cause high levels of aggression in children, this study suggests that 1 year of parental leave, and entry into high-quality center care thereafter, may help prevent such an outcome,” the researchers write.

Given the evidence that early child care is not associated with problems with aggression, the researchers are turning their attention to the potential positive effects that daycare may have for children’s language development and learning.

This research was funded by two grants from the Research Council of Norway (Grant Nos. 202438/S20 and 234828/H20).