The roll count is up at both Cromwell College and Alexandra's Dunstan High School.
Cromwell College principal Mason Stretch said the secondary school was close to outgrowing its capacity.
Dunstan principal Reece Goldsmith said it was "probably the largest roll in over a decade''.
Mr Stretch said the roll count of Cromwell's only secondary school was 505, an increase of 48 pupils in less than a year.
"We have little flexibility with rooms now; it is tight.''
Mr Stretch confirmed the 100 new year 7 pupils who began at Cromwell College were the ``largest intake since the 1980s''.
An additional teacher has been employed at the college as years 7 and 8 classes expanded from three to four.
Thirty-five new students across the year levels were made up of "those in the school's Apartments Boarding programme, international students and those new or returning to Cromwell''.
A high priority for the school has been collaboration with the Ministry of Education on a master plan to accommodate surging numbers.
Mr Stretch confirmed the school had had several meetings with the ministry and had recently met an architect to scope school buildings. A business case and education brief would be developed "over the next eight months''.
"This needs to be completed and approved before any build.''
Ministry sector enablement and support deputy secretary Katrina Casey said it had been monitoring the rolls of all schools in Central Otago and was aware of steady growth across both primary and secondary schools in Cromwell and Alexandra.
"We work closely with schools that have concerns about roll growth, to identify what options exist, and whether or not planning for additional classrooms is needed,'' Ms Casey said.
In Alexandra, Mr Goldsmith said the total roll count was 585. At March 1 last year, it had been 559.
Pupil numbers soared to "around 650 between the mid-'80s and mid-'90s''.
"Since then, the roll slowly declined to approximately the low 500s before a steady rise over the last decade with a strong rise over the last three years.''
Dunstan had absorbed a total of 135 year 9 pupils alone to begin the term.
Mr Goldsmith said the year 9 intake was "big for us'' but the school was "well resourced''.
"Around 35 students have arrived from out of our district. This was quite unexpected.
"Thankfully, we are fully staffed so we can cope.''
