Schools need to upgrade their furniture because today's children have outgrown the tables and chairs designed to meet the needs of 1960s pupils, experts say.

Pupils are so much bigger in height as well as girth that many no longer fit into standard school furniture.

There is also a much larger variation in the size of pupils meaning furniture needs to be redesigned to meet a wide range of shapes and sizes.

The recommendation is made in a wide-ranging report from the British Educational Suppliers Association, backed by the former education secretary Charles Clarke, which sets out the changing needs of schools.

It warns that schools are creating a generation of children who could suffer from back problems as the result of squeezing into ill-fitting furniture for hours every day.

Dominic Savage, director general of the Besa, said children are significantly taller now but that childhood obesity also contributed to the need for more ergonomic furniture in schools.

He said: "Although our starting point was not a question of obesity, when we looked, it is very much that the average child today is very different to a child in the 1960s, which is the last time children were actually measured for determining measures of furniture.

A study of 1,500 children found "significant" variation in their sizes, Besa said.

"Not only were children generally taller than their peers in the 1960s, but the range of heights in any age cohort was far greater. Crucially, another change was evident. The ratios of body to leg and arm lengths were different, meaning that accepted relative heights of chairs and tables were inappropriate," the report concludes.

"All of this data supported the belief that our children are likely to be spending thousands of hours of their school lives on chairs and at desks and tables where their posture is poor and the potential for damage to backs is great."

It is recommending a new standard size for school furniture which it wants the government to advise all schools to adopt. Adjustable furniture might be one option so children could lower or raise their chair to make sure they are sitting comfortably.