"It has not grown as much as we expected," she said "It's very difficult [to predict roll growth]. What we did was look at the last five years of retention percentage and we also look at contributing schools [like intermediate schools] and how many students might come to us from there, and base our predictions on that."
Ms Gilbert-Smith said transient students, students changing schools and a range of other factors meant sometimes that prediction was off, like it was this year. She said as a result the school had employed two too many staff.
"So we're about two people overstaffed and it is not ideal. If you ask teachers they will tell you [the current staffing] feels right."
The school gets Ministry of Education funding, based on the school roll size, for teachers' salaries.
"There is [also] board funded salary some schools use and we haven't used that and we prefer not to be in a position where we are forced to have that but the board have said they are open to maintaining current staff."
She said many Board of Trustees fund additional teachers from their own funds, if they have them, which may come from income generated through international students, for example. She said boards do this so they can offer a wider range of subjects or to have less students per class.
Ms Gilbert-Smith said despite the roll not reaching the number expected, the extra classrooms were needed with classes overflowing with students.
"What would happen is class sizes would increase and we would've just had insufficient space to manage so we needed these extra classrooms."
Ms Gilbert-Smith said there has been no date set for new classroom developments but said there was significant on-going work to be done between the Board of Trustees, the Ministry of Education and project managers Octa before anything else. She said she hoped there would be progress over the next year.