The 19-year-old entered the school assembly shortly before 9am beaming, her Olympic bronze medal slung around her neck.
McCartney has been rushing around the city since arriving back from Rio where her underdog bronze medal win in the women's pole vaulting event launched her profile in New Zealand.
The young Olympian told Belmont Primary pupils of her surprise and joy at having placed high enough to win a medal in Rio.
"It wasn't part of the plan, but it wasn't a bad thing," she said, laughing.
McCartney recalled the disbelief at realising she'd won after another athlete failed to clear the bar in the face-off for bronze.
"I realised I'd won a medal at the Olympic games and that was just..."
Being a relatively new athlete at the games meant part of her focus for Rio was about enjoying herself while she was there, McCartney said.
"I wanted to do well and that didn't take away from that but I was also enjoying [my time]."
As a child McCartney also attended Vauxhall Primary school on the North Shore, where she was school mates with Kiwi pop sensation Lorde.
Speaking to media this morning, McCartney said took her a while to process her Olympic bronze medal win.
"It actually did take me a little while because I was rushing everywhere - it was just one thing after another," she told TVNZ.
"We were just rushing to places and I was on the plane and I was off again. So it was nice to have a little break and I was able to think about everything and God, there was a lot to think about."
McCartney said all the air hostesses on the flight back knew who she was.
At Belmont Primary, the rising star said she hadn't yet thought about where she'd keep her weighty bronze medal now she was back home.
"There's a beautiful little box it came in but I haven't thought about it yet."
Speaking to Mark Sainsbury earlier, coach Jeremy McColl talked about how he had set up a Givealittle page to raise the money for new poles for McCartney and other young athletes.
When asked how much of their own money had been spent making McCartney's Olympic dreams come true, McColl said he dreaded to think about how high the number was - "I don't want to say."
McCartney's personal best, which she matched in her winning jump, is 4.80m. The world record is 5.06m and McColl has said he thinks she'll be clearing 5m within the next few years.
