Examples included: Do you know where your grandparents grew up? Do you know where your mom and dad went to high school? Do you know where your parents met? Do you know an illness or something really terrible that happened in your family? Do you know the story of your birth?

Dr. Duke and Dr. Fivush asked those questions of four dozen families in the summer of 2001, and taped several of their dinner table conversations. They then compared the children’s results to a battery of psychological tests the children had taken, and reached an overwhelming conclusion. The more children knew about their family’s history, the stronger their sense of control over their lives, the higher their self-esteem and the more successfully they believed their families functioned. The “Do You Know?” scale turned out to be the best single predictor of children’s emotional health and happiness.

“We were blown away,” Dr. Duke said.

And then something unexpected happened. Two months later was Sept. 11. As citizens, Dr. Duke and Dr. Fivush were horrified like everyone else, but as psychologists, they knew they had been given a rare opportunity: though the families they studied had not been directly affected by the events, all the children had experienced the same national trauma at the same time. The researchers went back and reassessed the children.

“Once again,” Dr. Duke said, “the ones who knew more about their families proved to be more resilient, meaning they could moderate the effects of stress.”

Why does knowing where your grandmother went to school help a child overcome something as minor as a skinned knee or as major as a terrorist attack?

“The answers have to do with a child’s sense of being part of a larger family,” Dr. Duke said.

Psychologists have found that every family has a unifying narrative, he explained, and those narratives take one of three shapes.