Andy and Jamie Murray were so competitive when they were children that they devised their own games and scoring systems when they were not playing in junior tennis tournaments.
Their mother has no doubts that this sibling rivalry and them taking part in competition from an early age helped drive both her boys to both become Wimbledon champions.
But Judy Murray has warned that Britain’s next generation of sporting heroes are being held back by schools insisting on holding non-competitive sports days where there are no winners or losers.
The 61-year-old tennis coach said getting rid of the competition element was robbing sporty children of their chance to shine and depriving them of the chance to learn crucial life skills.
Admitting that non-competitive sports days were "like a red rag to a bull for me", she argued that instead they should resemble this summer’s Olympics by having "medals and podiums" and "elation and disappointment".
More than half of the UK’s primary schools hold non-competitive sports days that fail to announce ‘winners’ despite around three-quarters of parents wanting "healthy competition" for their children, according to a survey conducted in 2017.
Amid fears that non-sporty children would be stigmatised or upset by defeat, pupils instead work in teams and are recognised for simply taking part.
Murray, who is heading to Wimbledon this week to watch her sons in action, said sports days, school concerts and art showings should be viewed as "opportunities to show where our skill sets lie."
Sir Andy Murray and his mum, Judy, arrive at Wimbledon last year. The pair and Sir Andy's brother Jamie will all return to Wimbledon this week
Credit: Paul Grover
"In Jamie and Andy’s early primary school years, sports days were proper sports days. You won little rosettes or mini medals if you came first, second or third," she wrote in the Sunday Post.
"I remember so clearly when that changed, when sports days stopped being competitive and were turned into some giant obstacle course where everyone got a sticker at the end.
"I had that incredible sense of disappointment that kids were being deprived of the challenge of the 50m sprint and the egg ‘n’ spoon or sack races.
"Obviously I am sporty and I am competitive, but life is competitive and we have to prepare kids for what life will throw at them."
She said children have "different skills sets and interests" and schools have a responsibility "to develop opportunities for these to develop and thrive."
In a report commissioned after the 2012 Olympics, Sir Michael Wilshaw, Ofsted’s then chief inspector, said state school headteachers needed to stop treating competitive sport as an "optional extra."
The report found that in the most successful schools, both state and private, heads recognised that competitive sport could help build an ethos and increase pupils’ grades. However, only 13 per cent of heads said they expected all pupils to take part.
"My boys always enjoyed competing with each other and they were always creating fun games at home, making up their own rules and scoring systems," Murray said.
"The fun of sport is all about the playing of the game and enjoying the challenge of the competition. Sports develop life skills like no other activity.
"If you watch the Olympics on TV this summer, you know there have been heats and trials to qualify for the final stages. You know there are medals and podiums and there is elation and disappointment.
"Shouldn’t our school sports days be mini replicas of what you see on the telly? Isn’t that how you light a spark?"
Sir Andy, 34, has previously described how he and his brother "were always competing against each other" at tennis, table tennis, squash, golf and football during their upbringing in the Scottish town of Dunblane.
He admitted that Jamie, who is 15 months older, "won most things we did" when they were really young but they were "pretty close really at most things" as he got older.
In 2013 Sir Andy became the first British winner of the men’s Wimbledon singles title since Fred Perry in 1936 and won it again three years later. He also won the US Open and the men’s singles Olympic gold, both in 2012.
Jamie has won seven Grand Slam doubles titles including the mixed doubles at Wimbledon in 2007 and 2017.