Demountable classrooms were introduced to NSW in the 1960s and '70s to accommodate another baby boom - the children of the first wave of post-war baby boomers - and have continued their steady march across school grounds and ovals ever since.
There are now 4950 demountable classrooms in NSW, comprising about 12 per cent of all classrooms, with double-storey demountables in some schools where space is at a premium, such as Artarmon and Chatswood public schools.
But rather than the ''hot tin cans'' described by the NSW Opposition Leader, John Robertson, today's demountables are well insulated and airconditioned.
The owner of Decentralised Demountables, Robert Wilson, who supplies buildings to public and private schools, believes they are unfairly demonised. ''They are insulated, we can make them to the same quality as bricks and mortar in terms of thermal quality, acoustic quality and, to a degree, aesthetic quality,'' he said. ''I know of teachers who prefer to teach in the classrooms we make.''
Mr Wilson has been supplying demountables for 32 years and has seen demand for the buildings grow as schools with limited space experience population growth.
Docomomo Australia, based at the University of Melbourne's faculty of architecture, building and planning, has documented the demountable since the first one was established at Kingsgrove North High School in 1966.
The group believes they are architecturally significant, as ''an important example of post-war prefabrication'', noting that the ''divisible mobile classrooms were designed in NSW and include sun shading devices''.
About 500 demountables were replaced under the federal government's Building the Education Revolution program.
A plan to replace the remaining demountables was scrapped by the NSW government because of its $1.5 billion cost.