Primary schools in Sydney's north are so overcrowded that the state government has considered buying land and redeveloping it into residential blocks with classrooms underneath to cope with ballooning enrolments.

Schools on the north shore are so full that many, including Artarmon, Northbridge and Chatswood, are well above capacity and at Willoughby Public there are more than 2000 students on a site shared with Willoughby Girls High. The three hectare site was designed to accommodate just 450 students.

Parents of children attending Willoughby Public School are concerned that the school is on land meant for 450 students but has more than 1000 with more expected. Credit:Wolter Peeters

Enrolments at the primary school have grown 37 per cent in just eight years, and this year there are 1044 students at the school.

Last year, a working party developed a plan for the Department of Education to buy properties and vacant land next to the school on Penshurst Street, with extra classrooms to be funded by a commercial development, most likely to be residential units.