Every Kiwi who visits a city like London or New York has felt a shudder at the first sight of a school in a concrete jungle.
First, the familiar shrieks of children at play are heard above the hum of traffic. Then, between a break in the buildings, there is a momentary glimpse of the children playing in a small patch of asphalt behind iron railings.
The image is so fleeting the New Zealander is liable to glance back and wonder, was that a school?
How different the picture has been here. Our idea of a school is a collection of low-lying buildings spread comfortably around a playground and likely to be surrounded by so much green field they command their own park.
But for how much longer? Expansive green playing fields may be one of those traditional items of "Kiwiana": images and values that have long helped to define us but, rightly or wrongly, may have had their day.
In Auckland, at least, population growth is putting relentless pressure on school facilities and prefabricated classrooms are steadily encroaching on playing fields.
Last Sunday we reported that the Ministry of Education estimates 200 extra classrooms will be needed in the city within four years to accommodate an additional 5400 children.
The takeover of playing fields by "prefabs" is supposed to be only temporary, but green space, once lost, has a way of disappearing for good. People become accustomed to a diminished area and "temporary" buildings can seem more useful than cleared ground.
Most Aucklanders are in no position to criticise this trend. Around our homes these days few of us have the expanse of lawns and gardens that previous generations valued.
We have divided the old quarter-acre section, sold the back lot and built a bigger house with double garaging and paving that practically covers the yard.
We put a higher value now on space for inside activities: computers, wide-screen TV, entertaining. We want walk-in wardrobes, en suite bathrooms, built-in barbecues, decks and jacuzzis, not trees and lawns.
But even as we forsake the outdoors we romanticise its values (How many really still have a garden shed?) and we object to city plans that encourage higher-density development. We may have subdivided the section but we do not want apartment blocks in the neighbourhood.
Our population, though, is not only growing - it is changing. Immigrant communities are more accustomed to apartment living and patronising the public transport that more dense residential development can support.
The school playgrounds diminishing before our eyes are a symptom of urban intensification that is probably impossible to resist.
The best we can do, to ensure our children's children go to schools with green grass and sports fields, may be to see that those facilities are better used.
The idea that school grounds and buildings should have more community use is not new. In England, governments have built new schools with theatres, gyms and fields - then made those facilities available to the wider communities outside class hours.
But in New Zealand, the idea has not had much urgency in an era of plentiful suburban parks, reserves, swimming pools, golf courses and sports clubs. Schools have been doing away with pools and making more use of public facilities for many outdoor activities.
It is time now to return our towns' green spaces to the children. Schools have a special place in a community.
If we want to preserve the values of open space and outdoor activity in the minds and hearts of our kids, schools need to keep their playing fields. They may be more precious than we know.