Then last spring, the psychologist treating Michael referred his parents to Dan Waschbusch, a researcher at Florida International University. Following a battery of evaluations, Anne and Miguel were presented with another possible diagnosis: their son Michael might be a psychopath.

For the past 10 years, Waschbusch has been studying “callous-unemotional” children — those who exhibit a distinctive lack of affect, remorse or empathy — and who are considered at risk of becoming psychopaths as adults. To evaluate Michael, Waschbusch used a combination of psychological exams and teacher- and family-rating scales, including the Inventory of Callous-Unemotional Traits, the Child Psychopathy Scale and a modified version of the Antisocial Process Screening Device — all tools designed to measure the cold, predatory conduct most closely associated with adult psychopathy. (The terms “sociopath” and “psychopath” are essentially identical.) A research assistant interviewed Michael’s parents and teachers about his behavior at home and in school. When all the exams and reports were tabulated, Michael was almost two standard deviations outside the normal range for callous-unemotional behavior, which placed him on the severe end of the spectrum.

Currently, there is no standard test for psychopathy in children, but a growing number of psychologists believe that psychopathy, like autism, is a distinct neurological condition — one that can be identified in children as young as 5. Crucial to this diagnosis are callous-unemotional traits, which most researchers now believe distinguish “fledgling psychopaths” from children with ordinary conduct disorder, who are also impulsive and hard to control and exhibit hostile or violent behavior. According to some studies, roughly one-third of children with severe behavioral problems — like the aggressive disobedience that Michael displays — also test above normal on callous-unemotional traits. (Narcissism and impulsivity, which are part of the adult diagnostic criteria, are difficult to apply to children, who are narcissistic and impulsive by nature.)

In some children, C.U. traits manifest in obvious ways. Paul Frick, a psychologist at the University of New Orleans who has studied risk factors for psychopathy in children for two decades, described one boy who used a knife to cut off the tail of the family cat bit by bit, over a period of weeks. The boy was proud of the serial amputations, which his parents initially failed to notice. “When we talked about it, he was very straightforward,” Frick recalls. “He said: ‘I want to be a scientist, and I was experimenting. I wanted to see how the cat would react.’ ”

In another famous case, a 9-year-old boy named Jeffrey Bailey pushed a toddler into the deep end of a motel swimming pool in Florida. As the boy struggled and sank to the bottom, Bailey pulled up a chair to watch. Questioned by the police afterward, Bailey explained that he was curious to see someone drown. When he was taken into custody, he seemed untroubled by the prospect of jail but was pleased to be the center of attention.

In many children, though, the signs are subtler. Callous-unemotional children tend to be highly manipulative, Frick notes. They also lie frequently — not just to avoid punishment, as all children will, but for any reason, or none. “Most kids, if you catch them stealing a cookie from the jar before dinner, they’ll look guilty,” Frick says. “They want the cookie, but they also feel bad. Even kids with severe A.D.H.D.: they may have poor impulse control, but they still feel bad when they realize that their mom is mad at them.” Callous-unemotional children are unrepentant. “They don’t care if someone is mad at them,” Frick says. “They don’t care if they hurt someone’s feelings.” Like adult psychopaths, they can seem to lack humanity. “If they can get what they want without being cruel, that’s often easier,” Frick observes. “But at the end of the day, they’ll do whatever works best.”

The idea that a young child could have psychopathic tendencies remains controversial among psychologists. Laurence Steinberg, a psychologist at Temple University, has argued that psychopathy, like other personality disorders, is almost impossible to diagnose accurately in children, or even in teenagers — both because their brains are still developing and because normal behavior at these ages can be misinterpreted as psychopathic. Others fear that even if such a diagnosis can be made accurately, the social cost of branding a young child a psychopath is simply too high. (The disorder has historically been considered untreatable.) John Edens, a clinical psychologist at Texas A&M University, has cautioned against spending money on research to identify children at risk of psychopathy. “This isn’t like autism, where the child and parents will find support,” Edens observes. “Even if accurate, it’s a ruinous diagnosis. No one is sympathetic to the mother of a psychopath.”