De Ridder (15) won gold in the under-55kg junior men grade and in the under-55kg cadet grade.
A member of the Renshuden club, he was the most successful of the Dunedin competitors who went to the championships.
Dylan Murcott (14), also of the Renshuden club, won a bronze in the junior men’s under-70kg grade, alongside club members, Ben Sinclair (11), who won a silver in the under-36kg senior boys, Patrick Craft (11), who won a bronze in the under-32kg senior boys, and Ron Williams (66), who won silver in the masters, under-90kg grade.
From the Kaikorai Valley club, Tessa Brownlie (14) won bronzes in the senior girls open and senior girls under-60kg grade.
Also from the Kaikorai Valley club was Kruz Cleminson, who won bronze medals in the under-81kg cadets and junior men’s.
The medallists were coached by Williams and Ron Craft.