At 4ft 3ins, Zander Fitzsimmons, from Cumbernauld, is already as tall as a 10-year-old and towers above his P1 classmates, including best pal Scott Gibson, who is 3ft 6ins.
Mum Kelly is continuously replacing his shoes and clothes as he grows so quickly.
Zander's shoes are a size one, only two sizes smaller than his mum, and he gets turned away from soft play areas for being too tall.
Amazingly, at 5ft 2 and 5ft 5ins respectively, both his parents, Kelly, 22, and Adam, 24, are smaller than average.
And there is no history of tall children in the family.
Zander was born five weeks premature, weighing 6lbs. By the time he was a toddler, he was already taller than all his nursery friends.
Kelly said: "We noticed it in nursery really. He's always been aware of it.
"He towers over his friends. If there is any trouble in school, he's always the one that gets noticed.
"Sometimes parents think he's older than he is, they will say, 'He shouldn't be talking like that'. But he's only five."
However, Kelly says his two-year-old brother Max has a bigger appetite. "Zander likes good food like steak and fish, but he doesn't eat a lot of it."
Doctors think Zander, who is a pupil at Condorrat Primary School, will reach the lofty heights of 6ft 6in, just an inch shy of footballer Peter Crouch.
Kelly said: "We are really hoping that Zander is the UK's tallest boy as it would be nice for him to have something positive about his height."
The average height of a five-year-old boy is 3ft 7ins.
Two years ago the record was set by a five-year-old boy who measured 4ft 2ins tall.
The record for the tallest girl in the UK is throught to have been set by Liana-Jean Lisle, from South West London, who measured 4ft 7ins at the age of five.