Simon Armstrong, a year 11 pupil at Blessed Edward Jones High School in Rhyl, passed his Royal Schools of Music grade five exam with high distinction.
Although Simon has played the clarinet for several years, this was his first exam and he responded by scoring 29 out of 30 for all three performances and a maximum 21 out of 21 for his sight reading.
Headteacher Catherine Britton believes Simon's success is reflective of the strides being made to improve the school's reputation.
She said: "Any of our young people who show aptitude are encouraged to achieve in the new style Blessed Edward's. Children who speak another language or who study out of school are given every opportunity to achieve accredited success.
"We will continue our excellence in education programme and enjoy our newly found popularity. More than 20 pupils have transferred to Blessed Edward's since I have been here. The school continues to go from strength to strength."
Simon was coached for the exam by locally-based clarinet player Dave Hopkins.