Parents who push their children to be 'perfect' are damaging them, says a leading headteacher.
Instead, mums and dads should stop pushing their kids to gain top marks and accept their children are 'good enough'.
The call comes from Heather Hanbury, head of the Lady Eleanor Holles School in Hampton.
Writing in Attain, the magazine of the Independent Association of Prep Schools, she said: "'The search for perfection is the enemy of achievement' is a quote I use regularly. In most areas of life (although not all), five things done adequately are more valuable than one thing done perfectly.
"I might even add to the aphorism: the search for perfection is the enemy of achievement and of self-esteem. Inevitably, searching for perfection ends in frequent disappointment.
She said spending less time perfecting homework means pupils can develop creative, sporting or other activities outside the classroom.
Ms Hanbury added: "The wider the variety of activities children try, the greater chance they have of finding something which truly rewards their efforts and helps to raise their self-esteem."
She also said spending double the amount of time required on homework, trying to perfect it, may not even be worth a pupils' time.
She said: "Think of the opportunity costs involved: what wasn't done because of the time spent on one essay?
"Taken to its extreme, I have known students who wouldn't hand work in at all because they said it wasn't good enough – when pushed they admitted they wanted to hand in something which was perfect.
"So instead of gaining 60 per cent or 70 per cent for an 'imperfect' homework, they gained 0 per cent for no homework."
She said: "Pupils in high-achieving schools, and their parents, often assume that anything below A or 1 is simply not good enough.
"Teachers feel the pressure to ensure that the majority of their pupils achieve high marks – so they may make tests or homework easier, or mark them more gently. They don't want their pupils to be dejected and upset when they don't get an A grade."
But she said this culture needed to see a shift in the opposite direction. So rather than making it easier for pupils to get higher grades, getting a B - or a C grade - should be seen as 'normal'.
She added: "For those who struggle with a subject it might be a real improvement and a step in the right direction; for those who find it easier, this may be a blip in their otherwise speedy progress, to be expected from time to time if they are challenging themselves to achieve more."