Experts say the surge in secondary school students has been spurred by the baby-bonus generation coming of age, interstate migration and a healthy economy.

New analysis by the Grattan Institute reveals that between 2018 to 2024, Victorian secondary schools will have to squeeze in an extra 10,900 students each year. This is roughly equivalent to seven large high schools of students.

Between 2007 and 2013, in comparison, there were 1600 extra students per year – or the population of one high school.

“That’s a huge jump,” the Grattan Institute’s school expert Pete Goss said.

“Those students will then want further education or a job, and we’d better start getting ready for how we are going to support them all.”

The mini baby boom hit primary schools in 2011/12 and is now being felt in secondary schools, which are recruiting extra teachers, rolling out portables and staggering lunch times to ease the pressure.

The Andrews government promised ahead of the recent state election that it would build 100 new state schools to accommodate the growth.

Figures obtained from the Education Department show that 76,200 students are predicted to start year 7 at state, Catholic and independent schools next year, up from 65,363 students in 2014.

The growth is more pronounced at state schools, where year 7 enrolments have increased by 21 per cent since 2014. This is twice the rate of the growth of year 7 enrolments at non-government schools.

Dr Goss said the student boom coincided with the peak of the baby-bonus scheme, a federal government initiative that ran between 2004 and 2014 and gave parents up to $5000 for each baby.

Former treasurer Peter Costello famously egged on couples to “have one for mum, one for dad and one for the country”.

A healthy economy and interstate migration to Victoria have also fuelled the influx of students.

“The economy has also been going very well for a long time, which may give people confidence to have more children,” Dr Goss said.

Current trends suggest that the growth in secondary school students could stabilise at about 77,000 enrolments from 2020 onwards, Dr Goss said.

At Mount Alexander College in Flemington, year 7 enrolments will hit 130 students next year. This is up from 36 students just two years ago and will mean the school has to run two extra classes.

Grade 6 student Ziggy, who will travel from West Footscray next year to attend high school, said he had heard good things about Mount Alexander College from his big sister, who is in year 8.

"She loves it," he said.

The school has no school bells, no set year levels for electives and gives students a much greater say in their learning.

Principal Wayne Haworth said the boost in enrolments was due to increased public confidence in the multicultural state school.

“Word of mouth over the past few years has made families have a second look at the school,” Mr Haworth said.

Matthew Deakin, the chief demographer at .id the Population Experts, said graduating year 12s were being replaced by much larger year 7 cohorts.

He said there were almost 15 per cent more students in year 7 than in year 12.

He said more flexible workplaces and increased access to childcare were also driving this growth.

“That sense of confidence, that things are going to be OK, is incredibly important when you have children," he said. "People are so incredibly rational now.”

Melton Secondary College west of Melbourne is also grappling with an influx of students.

Next year, year 7 enrolments will increase from 180 to 250 students.

In just six years, the school has almost doubled in size to 1150 students.

“It’s very tight,” principal David Reynolds said.

In order to save space, the school is running literacy and numeracy intervention classes in hallways and always runs two classes in the library.

Victorian Education Minister James Merlino said he had been preparing for the student boom for some time.

“For too long, there was not a long-term plan for new schools and that is why we have a plan to open 100 new schools over the next eight years to ensure we meet this growth,” Mr Merlino said.

"This will give us the opportunity to get ahead of the growth rather than playing catch-up.”