She was then asked to the stage, alongside her mother, to receive her NZ Flag Envoy jumper, amid cheering and applause from her classmates.
When Carter, who is ANZ's Olympic Ambassador, asked her how she felt she said: "I'm speechless."
The competition drew more than 16,000 entries and was open to all ANZ customers.
Tayla will travel to Wellington tomorrow to pick up the flag.
She will fly to London with her mum and grandparents to present the flag to the Governor-General and the New Zealand Olympic team, on July 26.
The teenager had been attending Rangitoto College for less than two weeks and said she was "overwhelmed" by the win, having never been to London before.
Carter said it was great to see the Olympics connecting the country.
"New Zealanders get really close to it, they follow the team. And if you get to see them it's so much more real."