Here is an experiment you don’t want to try at home.

Show a toy to a toddler and explain that it’s something special you’ve had since you were little. Ask the child to be “very careful” with it. Hand over the toy, which appears to be in fine condition, except that you’ve secretly rigged it to break spectacularly as soon as the child handles it.

When your precious toy falls apart, express regret by mildly saying, “Oh, my.” Then observe the child.

The point is not to permanently traumatize anyone - the researchers who performed this experiment quickly followed it with a ritual absolving the child of blame. But first, for 60 seconds after the toy broke, the psychologists recorded every reaction as the toddlers squirmed, avoided the experimenter’s gaze, hunched their shoulders, hugged themselves and covered their faces with their hands.

It was part of a long-term study at the University of Iowa to isolate the effects of two distinct mechanisms that help children become considerate, conscientious adults. One mechanism is called effortful self-control - how well you can think ahead and deliberately suppress impulsive behavior that hurts yourself and others.

The other is less rational and is especially valuable for children and adults with poor self-control. It’s the feeling measured in that broken-toy experiment: guilt, or what children diagnose as a “sinking feeling in the tummy.”

Guilt in all its varieties - Puritan, Catholic, Jewish, et cetera - has often gotten a bad rap, but psychologists keep finding evidence of its usefulness. Too little guilt clearly has a downside, most obviously in sociopaths who feel no remorse, but also in kindergartners who smack other children or snatch their toys.

Children typically start to feel guilt in their second year of life, says Grazyna Kochanska, who has been tracking children’s development for two decades in her laboratory at the University of Iowa. Some children’s temperament makes them prone to guilt, she said, and some become more guilt-prone thanks to parents and other early influences.

“Children respond with acute and intense tension and negative emotions when they are tempted to misbehave, or even anticipate violating norms and rules,” she said. “They remember, often subconsciously, how awful they have felt in the past.”

In her latest studies, published in the August issue of The Journal of Personality and Social Psychology, she and colleagues found that 2-yearolds who showed more chagrin during the broken-toy experiment went on to have fewer behavioral problems over the next five years.

Even children who were low in guilt still behaved well if they had high self-control. “Even if you don’t have that sinking feeling in the tummy, you can still suppress impulses,” Dr. Kochanska said.

But what if your child lacks both self-control and guilt? What can you do? And should you feel guilty for doing a lousy job of parenting?

You could blame yourself, though researchers haven’t been able to link any particular pattern of parenting to children’s levels of guilt, says June Tangney, a psychologist at George Mason University in Virginia.

But Dr. Tangney, who has studied guilt extensively in both children and adults, including prison inmates, does have some advice for parents.

“The key element is the difference between shame and guilt,” she says. Shame, the feeling that you’re a bad person because of bad behavior, has repeatedly been found to be unhealthy, she says, whereas guilty feelings focused on the behavior itself can be productive.

But it’s not enough, Dr. Tangney says, for parents just to follow the old admonition to criticize the sin, not the sinner. “Most young children really don’t hear the distinction between ‘Johnny, you did a bad thing’ versus ‘Johnny, you’re a bad boy,’” she said. “They hear ‘bad kid.’”