He was in year 12 at King's when he was diagnosed in September 2015.
Nearly 400 people attended his funeral at the school and there was standing room only in the King's & Queen's Performing Arts Centre during the service of nearly two hours.
Family and friends spoke of Mitch as a leader, a mentor and defiant until the end.
Tributes mentioned his strength, courage, humility, grace and dignity.
Tears flowed as people remembered his smile and laugh.
The song Lay Me Down, by Sam Smith, was performed at the service and as the coffin was carried to the hearse, the song Stand By Me by Ben E. King was played.
Pupils performed a haka as the hearse left the school grounds.
In the days before the funeral, acting deputy rector Darin Smith said pupils and staff were ''devastated'' by the news of Mitch's death.
''They're hurting, but I've said to the staff, 'Let's keep an eye out for the boys and let's look after each other'.''
Mr Smith said they had been inspired by Mitch's calmness and dignity in the face of adversity.
Since his diagnosis, Mitch had been living in Invercargill with his mother, Ana, and siblings Anthony, Mya, Nthswana and Neo.
