The psychologist Kang Lee, who has been researching deception in children for more than two decades, likes to tell parents that if they discover their child lying at age 2 or 3, they should celebrate. But if your child is lagging behind, don’t worry: You can speed up the process. Training children in executive functioning and theory of mind using a variety of interactive games and role-playing exercises can turn truth-tellers into liars within weeks, Professor Lee has found. And teaching kids to lie improves their scores on tests of executive functioning and theory of mind. Lying, in other words, is good for your brain.

For parents, the findings present something of a paradox. We want our children to be clever enough to lie but morally disinclined to do so. And there are times when a child’s safety depends on getting at the truth, as in criminal cases involving maltreatment or abuse. How can we get our children to be honest?

In general, carrots work better than sticks. Harsh punishments like spanking do little to deter lying, research indicates, and if anything may be counterproductive. In one study, Professor Lee and the developmental psychologist Victoria Talwar compared the truth-telling behaviors of West African preschoolers from two schools, one that employed highly punitive measures such as corporal punishment to discipline students and another that favored more tempered methods like verbal reprimands and trips to the principal’s office. Students at the harsher school were not only more likely to lie but also far better at it.

Witnessing others being praised for honesty, meanwhile, and nonpunitive appeals for the truth — for example, “If you tell the truth, I will be really pleased with you” — promotes honest behavior, Professors Lee and Talwar have found.

So does a simple promise. Multiple studies have shown that children as old as 16 are less likely to lie about their misdeeds, and the misdeeds of others, after pledging to tell the truth, a result that has been replicated widely. The psychologist Angela Evans has also found that children are less likely to peek at the toy while the researcher is out of the room if they promise not to. Curiously, this works even with children who don’t know the meaning of the word “promise.” Merely securing a verbal agreement — “I will tell the truth” — does the trick. By the end of infancy, it would seem, children already grasp the significance of making a verbal commitment to another person.

As for those childhood morality tales, you might want to skip the more ominous ones. Professor Lee and others have found that reading stories to children about the perils of deceit, such as “The Boy Who Cried Wolf” and “Pinocchio,” fails to discourage them from lying. Reading them the story of George Washington and the cherry tree, on the other hand, in which truthfulness is met with approval, does reduce lying, albeit to a modest degree. The key to fostering honest behavior, Professor Lee and his colleagues argue, is positive messaging — emphasizing the benefits of honesty rather than the drawbacks of deception.