"They are quite quick aren't they," Senior Constable Kath Goodman, of Dunedin, said.
Using her laser speed gun, she recorded grass karts reaching 55kmh on the 625m course's straight.
About 100 pupils from 14 Canterbury, Otago and Southland high schools took part in the 2009 Grass Karts Challenge at the Mosgiel college.
The competition encouraged pupils to build and race their own grass karts.
The annual event, which was now in its third year, was a way of encouraging more pupils into studying mechanical engineering courses and careers, spokesman Phil Bradshaw said.
Teams were awarded points for construction, appearance, and record-keeping on Friday, and on Saturday had a chance to add to their points tallies when they took part in a series of races.
"They really look forward to the racing side of things," he said.
Results. - Overall winner, Northern Southland College (Lumsden); BOC Gases Construction Trophy, Aurora College A (Invercargill); Repco Appearance Trophy, Northern Southland College; Southern Group Training record-keeping award, Northern Southland College; Blackwoods Paykels Performance Award, Rangiora High School A (Rangiora).
