The new £23 million Mearns Academy will be over its initial pupil capacity within two years of opening, according to a new forecast.
Projected figures have revealed the 640-pupil building in Laurencekirk, in line for completion next summer, could top its limit as early as 2016.
Aberdeenshire Council moved to reassure parents the 17-acre development on Aberdeen Road, which includes a community campus, can be extended to accommodate up to 840 pupils.
However, the data from a council report predicts the school will be more than 125% its opening capacity by 2018, while Mackie Academy in Stonehaven will reach 113%.
Mearns Community Council chairman James Stuart said the Laurencekirk site was designed for up to 840 and will simply require additional classroom space as it is required.
He added: “When the council went to the Scottish Government they only got money to replace the school at its existing capacity of 640 and they have had to come up with the rest themselves.
“The council will be looking at the (forecast) figures for the next five to 10 years to see if there is just a blip or if there is a need to extend further.
“The school has a very good reputation and takes children from Brechin and Edzell as well as the local area.”
Mackie Academy’s pupil count is expected to rise from 1,087 to 1,289 over the next five years, while Mearns Academy will go from 599 to 676.
A council spokesman said Mearns Academy will be built with a “core capacity” of more than 28% of current requirements.
He added: “This is intended to ensure that we can deal with any increase in demand for toilets, social spaces, canteen space.
“For our classrooms, we design the plans in such a way that we can increase classroom capacity if need be, in the most cost effective manner possible.
“We anticipate that we will be able to meet the needs of the families in our catchment area for many years to come.”
The figures to be considered by the council’s education committee on Thursday also reveal an anticipated capacity breach in some Mearns primary school rolls by 2018, including Dunnottar (154%), Johnshaven (127%), Laurencekirk (123%) and Marykirk (122%).
In his report, director of education Stephen Archer said measures are in place to combat the effects on primary schools.
He said an extension is planned for Laurencekirk Primary with extra temporary accommodation available at Dunnottar.
Mr Archer added: “The working capacity for Johnshaven is expected to accommodate the projected increase in roll, and the roll at Marykirk will be closely monitored over the coming years to see if the projected numbers are realised.”
Dunnottar’s school role is expected to rise from 220 to 302 by 2018, with Johnshaven going from 39 to 60, Laurencekirk from 307 to 372 and Marykirk from 37 to 57.
Across both Kincardine and the Mearns there will be an increase of 782 pupils, or 13.6%, across both the primary and secondary sectors.
The wider forecast for Aberdeenshire indicates an increase of 14.2% for primaries and 5% for academies. The statistics account for demographic factors such as birth rate and new housing.
Work on the new Mearns Academy, which will include facilities to be used by the community, started in September last year and is due for completion in June 2014.
The site will have a range of sports facilities, including a four-court games hall, gym and fitness suite, public library, community rooms and a police office.
The project is funded through the council’s capital plan, with a contribution of £9.74m from the Scottish Futures Trust.