Yes, you read that correctly. Twenty-first century children are able to wait longer for a reward than children of the same age a generation ago, and a generation before that. The new study shows that today’s preschoolers are better at what psychologists call self-regulation, which is the conscious control of one’s immediate desires—the ability to hold off and wait until the time is right.

Stephanie Carlson, the lead author of the paper and a professor at the University of Minnesota’s Institute of Child Development, knows that her findings will come as a surprise: “The implicit assumption is that there’s no way that kids can delay. They’re used to being gratified immediately and don’t know what it’s like to be bored anymore.”

But faithful re-enactments of the famous “marshmallow experiment” have upended that notion. The experiment was first designed in 1968 by Walter Mischel of Stanford University, with the participation of 165 children between ages 3 and 5 who were attending the university’s Bing Preschool. The set up was simple: Each child was left alone in a quiet room facing two plates of goodies. One plate held a single treat—one Oreo cookie or one marshmallow, for example—while the other plate had two.

The children were then told that the adult needed to leave “to do some work” but would return immediately if the child rang a bell. If that happened, the child was allowed to eat one treat. But if the child waited until the adult came back without being summoned, they could eat the larger portion. Watching through a one-way mirror, the experimenters saw whether the child licked or ate the treats while they waited, or controlled themselves until the researcher returned.

According to Dr. Carlson’s new paper, the same experiment was replicated in the 1980s, with 135 children attending the Toddler Center at Columbia University, and once again in the 2000s, with 540 children at preschools associated with the University of Washington and the University of Minnesota. As it turns out, preschoolers in this millennium were able to wait about seven minutes on average, one minute longer than preschoolers in the 1980s and two minutes longer than children in the 1960s. Over a span of 50 years, children of the same age were essentially getting better and better at controlling their impulses.

What accounts for this surprising development? “We’re trying to understand what changed…so that kids of similar backgrounds have increased their ability to delay gratification, despite expectations,” Dr. Carlson said. Improvements in nutrition and GDP might have had the effect of expanding children’s opportunities and cognitive horizons.

Parenting has also evolved. Contrary to popular belief, parents are spending more time interacting with their children than they used to. In the mid-60s, parents spent an average of 36 minutes a day teaching and playing with their children. By 1998, that figure had more than doubled, to 78 minutes a day. Parents have also become more focused on cultivating a child’s ability to make decisions for themselves. Perhaps most important is that, compared with 1968, many times more 3- and 4-year-olds are in preschool, and their teachers are better educated than ever before.

Important questions remain about the study’s findings. The children at the university preschools were mostly from white, educated, middle-to-upper class families. Their self-control is getting better all the time. But it remains to be seen if children from other backgrounds are also learning the crucial lesson that good things come to those who wait.