The state government revealed in April that it will spend $5 billion to build and expand public schools to cope with an extra 164,000 additional students in state schools by 2031. Tuesday's state budget is expected to have a focus on education spending. But the Opposition education spokesman, Jihad Dib, said the government had "failed by a long shot" to plan for the high school boom. "I think the state government thought that there would continue to be a drift to private schools in high school but the cost of living in Sydney and mortgage repayments means that people are really struggling and plenty are now staying in the public system," he said. When Joanne Balta and her family moved to the Ryde area seven years ago, her son Zac was in the catchment areas for four public high schools. But surging student enrolments, shrinking school catchment areas and an apartment boom have cut that number to one.

"We have only one choice: Marsden High, which needs $2.8 million worth of repairs to bring it up to scratch," Ms Balta said. Zac is among more than 1 million NSW babies born during the so-called "baby bonus boom" of 2004-14. The boom has seen unprecedented levels of overcrowding in the state's primary schools and with the oldest of the baby bonus generation turning 13 this year, the crisis is about to hit high schools.

In Ryde, high school enrolments grew 3.4 per cent between 2016 and 2017, four times faster than across greater Sydney, which increased by less than 1 per cent. Its high-school-age population (10-19 years) is projected to swell by 30 per cent by 2026, compared with 22 per cent growth across Sydney. With more families now living in apartments and the city in the midst of an apartment boom, new residential blocks have the potential to significantly increase the number of children within a school catchment area. "Are our kids just supposed to be the lost generation? The kids that get forgotten because the government didn't plan ahead?," Ms Balta said.

"Meadowbank has had 3000 units built over the past few years ... and down the road another 3000 are planned. It's not like you couldn't see this going to happen." In Waverley, high school enrolments grew 13 times faster than across greater Sydney between 2016 and 2017, and the area is facing projected growth of 30 per cent among the population aged 10-19. Licia Heath, eastern campaign manager for Community for Local Options for Secondary Education (CLOSE) said there had been a "perfect storm" in the eastern suburbs, which included the closure of high schools, a birth boom and new apartments being rapidly built. Ms Heath said the eastern suburbs urgently needed a new public high school to cope with "an explosion of student numbers". She said the group was calling for a NSW parliamentary inquiry into the need for a new school.

"When you have an increase in population and a decrease in social infrastructure, you are in dire straits," Ms Heath said. Several high schools in the east have closed in the past two decades, including Vaucluse and North Randwick. A spokesman for the education department said it "acknowledged the growth in these areas". Since 2011, 32 new or relocated public schools have been funded and 67 major upgrade projects announced, the spokesman said.

"Growth in Sydney will be met by the new inner Sydney high school in Cleveland Street and the upgrade to Alexandria Park Community School. This will increase capacity by 2000 students by 2022. These schools will reduce the pressures on the catchment areas of Balmain and Leichardt, and Rose Bay Secondary College," the spokesman said. "While there is existing enrolment capacity in high schools serving the Canada Bay area, additional capacity will be required in the next five years. The department has developed a strategic school infrastructure plan which is informing government decisions regarding enrolment growth across Sydney, including the Canada Bay area." High school enrolments in Camden grew six times faster than the Sydney average and the population aged 10-19 is projected to explode by 75 per cent in the decade to 2026. In the four years to 2017, primary school enrolments have risen by 25 per cent.