It was opened by Northland MP Mike Sabin.
"It was very special for me to come along and see the pride written on the children's faces,"
he said.
Board of trustees chairwoman Roz Clent said Thursday's opening celebrated both the new block and the end of a long rebuilding programme.
She praised the staff for their dedication and flexibility, and for keeping the children focussed despite working in a building site for the past five years. At various times they had to make do without a staffroom, administration building, library and hall, and had to move frequently between temporary rooms.
Principal Ken McLeay said he was delighted with the modern classrooms and large shade areas.
"You can really feel the difference when you walk into the new classrooms. As well as being warm and dry, they look great and the acoustics are amazing. The students are buzzing," he said.
The rebuilding at Riverview School is part of a nationwide programme which has repaired or replaced about 1600 buildings at 780 schools since 2009.
The total spent on fixing watertightness problems at Northland schools so far is about $6.8 million, with Riverview accounting for about half that total. The Year 1-6 school opened in 1987 has 350 pupils.