Ruth Kelly, Education Secretary, said the extra duties being taken on by staff under the school workforce agreement had prompted her to look at the change, which would apply in England and Wales.

“If teaching assistants and support staff are taking on more responsibility, we have got to make sure that they are fairly rewarded and this is something we will be thinking about,” she said.

Her comments came as a “complete surprise” to the National Employers’

Organisation for School Teachers (NEOST), which is expected to oppose any change. Classroom assistant salaries currently vary widely in different parts of the country from around pound;8,000 to pound;18,000, unions say.

A new grade of higher-level teaching assistant was supposed to push up pay with locally determined salaries expected to vary between pound;18-21,000. But so far only 8,600 training places have been made available.

The arrangement means that there are wide variations in pay levels in different parts of the country.

Last week at the annual conference of the Association of Teachers and Lecturers in Torquay, when Ms Kelly was asked if a national structure for staff was on her agenda, she said: “There is a real issue here and it is one that we have been thinking about a lot. We can, through the School Teachers’ Review Body, say what teachers should be paid. Teaching assistants are in a different position. It is really a question of whether the local authorities or schools implement national benchmarks as to whether they receive the appropriate wage.”

She said that bringing support staff into a national structure would not be a “quick fix” and would require a change in legislation.

“We would have to see whether a consensus could be commanded across other support staff working in schools,” she said.

Unison, the biggest support staff union, was already planning to lodge a joint national pay claim with the other support staff unions after Easter.

It will be based on grades paying teaching assistants between Pounds 10,326-pound;25,407 a year depending on their jobs, with added London weighting.

John Richards, Unison senior national education officer, said: “This is very encouraging. It chimes with what our members have been saying. We would welcome any discussions on improving support staff pay.”

A survey of the union’s local branches in February revealed that 83 per cent of those responding backed a national pay structure.

But Mike Walker, NEOST secretary, said: “This is a complete surprise to us.

We tried national pay rates until 1997 and they did not work. That is why there is local pay. We hope the Secretary of State talks to us about this soon.”