The straight-A pupils who do best at school can be the ones most lacking in the grit they need in adult life, according to a leading expert in resilience.

Angela Lee Duckworth, a psychology lecturer at Pennsylvania University, said she called such students "the fragile perfects" because they had not experienced failure before they arrived at university.

Dr Duckworth, whose TED talk has been viewed more than 7 million times, told the Bett show in London that a range of positive attributes were correlated with grit, including having a set of purpose and a growth mindset.

However, being a student who always got good grades was not one of them.

"Those kids who never have an opportunity to fail – I see them, as I teach at an Ivy League university," she said. "I call them 'the fragile perfects', because they've never gotten a B in their lifetime. They have been winners all the way through. And if you are a winner all the way through it's really hard to lose."

The challenge with such high-achieving pupils was introducing "disappointment in a way that is natural", Dr Duckworth said.

"We don't want to trip them up on purpose. But how do you introduce them to the discomfort that comes from being on the edge, the occasional failure and occasional setback in ways that will build them resilience for the long term?"

Some schools in the UK have already begun trialling ways to tackle this challenge. Wimbledon High School, a private girls school, gained publicity in 2012 after launching a "failure week" to help its high-achieving students become less fearful of making mistakes.

Dr Duckworth has created a questionnaire to help measure grit that asks respondents how much they agree or disagree with a list of statements, including "I am hard worker" and "My interests change from year to year".

However, she acknowledged there was currently no objective, reliable way that schools could measure grit across students of different age groups.

"Grit" has become an increasingly popular buzzword in education in recent years, alongside "growth mindset", a term introduced and popularised by another US psychology lecturer, Carol Dweck.

Dr Duckworth said that her work, and that of Professor Dweck at Stanford University, showed a strong connection between the two characteristics. "A growth mindset is one of the largest predictors of grit," she said.