Kids today are in no hurry to grow up.

Teenagers are increasingly less likely to engage in adult activities like drinking alcohol, working jobs, driving or having sex according to research from San Diego State University and Bryn Mawr College published in the peer-reviewed journal Child Development Tuesday.

With smaller families, longer life expectancy and after-school educational activities, today’s 18-year-olds are looking like 15-year-olds once did, according to Jean Twenge, professor of psychology at San Diego State University and the lead author on the study. She calls it a “slow-life strategy” where parents have fewer children, “but nurture them more carefully.”

The number of teenagers who tried alcohol between 2010 and 2016 dropped to 67% from 93% between 1976 and 1979. And the number that had earned money from working dropped from 76% to 55% over the same period. Teens who had engaged in sexual activity by the end of high school dropped 12% between 1994 and 2016.

The declines in adult activities were consistent across demographic groups, including gender, race, socioeconomic status, region, and in both urban and rural areas, suggesting a major shift is taking place.

The researchers examined how often teenagers engaged in activities that adults do and that children don’t, including dating, going out without parents and driving. They analyzed seven large surveys of 8.3 million 13- to 19-year-olds between 1976 and 2016. The surveys were nationally representative, reflecting the population of U.S. teens in terms of gender, race/ethnicity, socioeconomic status and geographic region.

While smaller family sizes and changing economic factors such as unemployment rate and median household income are among the causes, Twenge also points to the rise of technology. In her article “Have Smartphones Destroyed a Generation?” Twenge explores these questions further, pointing out that millennials are on the brink of a mental health crisis brought on by an explosive increase in time spent online.

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“The smartphone and social media has caused an earthquake of a magnitude we’ve not seen in a very long time, if ever,” she wrote. “There is compelling evidence that the devices we’ve placed in young people’s hands are having profound effects on their lives — and making them seriously unhappy.”

However, others say not all of these effects can be traced to the sudden ubiquity of smart devices. More research needs to be done on social media use to determine whether its impact is positive or negative, said Sarah Rose Cavanagh, associate professor of psychology at Assumption College. “You cannot simply observe two large cultural shifts and then decide that since they happened at roughly the same time, that one is causing the other,” she said.

The upside to teens growing up more slowly: The rate of teen pregnancy has fallen dramatically in recent years, according to the Centers for Disease Control and Prevention. Birth rates fell 9% for girls aged 15 to 17 year-on-year in 2015 and 7% for women aged 18–19 years during the same period. “Still, the U.S. teen pregnancy rate is substantially higher than in other western industrialized nations, and racial/ethnic and geographic disparities in teen birth rates persist,” the CDC said.

Many high-school students are turning to summer classes and community service to pad college applications instead of taking on summer jobs, MarketWatch reported earlier this year. And it’s not always for lack of trying: Some employers want more highly skilled workers given the rise in the minimum wage in many states.

The most recent study does not pass judgment on whether this delayed adulthood is good or bad. “Adulting is now a verb!” Twenge said. “Teens are safer and don’t grow up before they’re ready, but the downside is they may go to college or their first job without as much experience with independence. Economically that means they are dependent on their parents for longer.”