Burnside High School student Alex Gibson, 15, won the Top in the World award in the Cambridge International General Certificate of Secondary Education (IGCSE) Music after he completed the examination in November.
The year 12 student scored the highest standard mark in the world for an individual subject in the exam.
Alex - who took up playing the saxophone when he was 8 - composed several pieces for a maximum 30% of his grade.
His performance as a soloist and in a band comprised a further 30% and the final examination 40%.
The Cambridge IGCSE Music programme, run by the University of Cambridge, aimed to develop Alex's musical skills through listening, performing and composing.
Said Burnside High principal Scott Haines: "Alex’s dedication to musical excellence, countless hours of practice, and unwavering commitment to his craft have culminated in this outstanding result.
"This achievement speaks volumes about his talent, work ethic, and passion for music.
"It also reflects wonderfully on our teachers, particularly Dr Helen Renaud and our music department, who have supported and guided Alex throughout his musical journey at Burnside."
Said school head of music Chris Petch: "This is an outstanding achievement for Alex, who has already collected a number of regional and national awards for his saxophone playing since joining the school in 2022.
"As a member of Burnside's Specialist Music Programme, Alex is a great example of what is possible when natural talent is matched by relentless energy and a flawless work ethic, and we could not be prouder of him."
Haines believes Alex has "set a new benchmark for excellence at Burnside High School".
"And his achievement will inspire future generations of musicians and Cambridge students.
"We are incredibly proud of Alex and look forward to following his continued success.”
More than two million Cambridge students from 10,000 schools across 160 countries participated in the examinations last year.
The University of Cambridge is the world's third-oldest university in continuous operation
A ceremony was held to celebrate the achievement on Thursday at the University of Auckland.
