Education Minister Anne Tolley said the Government had decided "in principal" to build a new primary school between Queenstown and Arrowtown, to open in 2021.
As well, Wakatipu High School would phase out years 7 and 8 over the next two years and the school "may also have to move to a new site in the future".
The ministry expects more than 1000 extra pupils will live in the Queenstown Lakes district by 2026 and the present schools will not be able to cope.
Ms Tolley said the change at the high school would ensure enough space for at least 10 more years, by which time planning would have been done to relocate it.
But board of trustees chairman Peter Doyle said a new high school needed to be built now.
There was not 10 years' capacity left.
"The board has been telling the ministry to find a new high school location for years.
"The predictions are that by end of 2015 we would have over 1000 kids, without years 7 and 8 included. To say we have another 10 years up our sleeves is ridiculous."
The Remarkables Primary School, being built now, has been designed for a roll of 460 and principal Debbie Dickson said it did not have space for more than about 500.
Queenstown Primary School principal John Western said the school would be nearing its capacity by the end of the year.
"I imagine in the timeframe suggested, it will be highly likely Queenstown Primary will again be overcrowded and all primary schools overcrowded by 2021."
St Josephs School principal Trisch Inder expected her school's roll to reach the cap of 160 by the end of the year.
Arrowtown Primary School principal Robin Harris said enrolment had more than doubled since the school was built 11 years ago.
New classrooms were added as demand increased and a junior classroom was to be built next year.
"There's pressure on facilities. We're getting to the stage where we're not able to accept out-of-zone enrolments, but we will be accepting siblings of existing pupils."
The ministry said information about potential sites for a new school was "commercially sensitive".
A location near Lake Hayes has been discussed in the past.
Queenstown Lakes Mayor Clive Geddes said the council would consider another land swap with the ministry, as was offered three years ago when the Remarkables Primary School proposal was being developed.
