"It helps to know why a child has committed a certain crime because it provides a guide to rehabilitation. It's like seeing a doctor and having a physical to determine if you require treatment," said Li Meijin, an expert in criminal psychology at the university.

"After talking to young criminals and testing them, we submit a report to the court which informs the judges whether the offender is likely to respond to a rehabilitation program."

Some minors who impulsively commit serious crimes, such as intentional homicide or intentional injury, can be rehabilitated via lenient punishment, while others require regular checks or long-term treatment to work through their problems, according to Li. "That's because they are likely to develop serious psychological problems, or have been deeply influenced by broken families or terrible backgrounds," he said.

Qin said psychological assessments can help judges during sentencing. She cited an example from 2015, when she sentenced a 17-year-old boy to two years in prison for injuring a stranger by stabbing him with a knife during a quarrel.

"The tests indicated that it was an impulsive act. Moreover, the offender pleaded guilty with a positive attitude, saying he did it to vent his anger," she said.

However, she sentenced another 17-year-old to 11 years for unintentional homicide and injury because he displayed no remorse and refused to apologize to the victims or their families.

"He injected bottles of juice with deadly chemicals with the aim of killing his step-grandmother after hearing his parents' complain that she would inherit his grandfather's property and goods," she said.

The boy's mother threw the bottles away before the step-grandmother could drink from them, but a 6-year-old boy died and an elderly woman was poisoned after drinking the juice.

No action was taken against the mother because she was unaware that the bottles contained lethal substances.

Parenting classes

Guo Jie, a judge from Fujian province, said the guardians of young defendants should be required to attend "good parenting" classes. "Insufficient care and protection, or poor communication within families can easily affect a child's behavior," she said.

A number of surveys reinforce that point. Between April and September, Song's team questioned 399 juvenile inmates, receiving 393 responses. More than 74 percent said their guardians did not provide adequate care and failed to offer guidance that would help them to avoid pitfalls.