If there were no unforeseen issues during the construction period, that timeframe would lead to completion early in the second term of 2010, board of trustees chairman John Watherston said.
The Ministry of Education has confirmed funding for the school.
After five years of negotiations, the board was relieved at the news.
Waitaki Valley School opened in 2004 on the Kurow Area School site after the merger of the Hakataramea Valley, Otematata and Kurow schools.
As it was previously an area school, many of the buildings were designed to suit the needs of secondary school pupils.
The outdated main block, housing classrooms and the administration area, was built in 1940.
Mr Watherston praised the efforts of the previous board for its "focus and tenacity" between 2004 and 2007 when dealing with the issue.
He also thanked principal Helen Blick and staff for putting up with "less than ideal" teaching facilities at times.
Pupils would shift to surplus buildings during construction, he said.
