Teachers are more likely to be fooled by pupils who deliver an outright denial that they have broken school rules than by those who make up elaborate excuses.
Research has provided new insight into how adults are taken in when children try to deceive them.
The study, from the University of California at Davis, concludes that adults are readily convinced when a child denies outright that an event has taken place. But it also shows that adults are significantly better at detecting when children invent information about an event that has not happened.
More than 100 adults were asked to watch videos of three-year-olds and five-year-olds talking about real-life and fictitious events.
The children were asked either to confirm or deny real-life events. They were then asked to do the same with fictitious events. Then the adults rated their truthfulness.
The majority could detect when children were making up accounts of fictitious events, But most believed children were telling the truth when they argued that real events had not taken place.
Charles Ward, general secretary of the Association of Educational Psychologists, said: "If you're making something up, you have to make it sound genuine," he said. "So it's easy for adults to question a story that a child presents."
Chris Davis, of the National Primary Headteachers' Association, agrees that some lies are easier to detect than others.
"Concocted stories usually fall apart," he said. "If children have cooked something up, they'll often try to embellish as they go, and tie themselves in knots. There's an honesty in some kids' eyes, and `I dare you to challenge me' in others'. But sometimes you're almost walking on eggshells, teasing out the veracity. You use your experience of how kids react."
But the implications of the research are more significant than creating adult scepticism around stories of homework-ingesting canines. Children who are victims of maltreatment or abuse could be overlooked because their denials are immediately believed.
Gail Goodman, one of the authors of the report, said: "Accurately detecting false reports protects innocent people from false allegations. But the failure to detect false denials could mean that adults fail to protect children."
But Trish O'Donnell, of the NSPCC, believes an inability to spot children's untruthful denials should not prevent teachers from identifying problems.
"It's not about asking direct questions," she said. "It's about the culture of the school and the classroom. It's about showing children that they can depend on you and trust you. And it's about opening up dialogue and making it OK to talk about things."