Investment in schools is being threatened by Britain's largest teaching union, the NUT, the government said yesterday.

Ministers have set a deadline of next Wednesday for agreement on reforms tied to the money, which schools are scheduled to receive over the next three years.

The National Union of Teachers, which has 220,000 members, is refusing to agree to plans to allow them a day off a fortnight for marking and preparation because it depends on their allowing unqualified assistants to take over certain lessons.

Schools minister David Miliband on Wednesday pledged to continue with plans to use classroom assistants despite opposition from unions.

Forum Response: Professional Association of Teachers

Deborah Simpson, senior professional officer for PAT, said: "The reform proposals currently being discussed by the DfES and the unions represent a major step forward in reducing teachers' workload and promoting a whole team approach of professionals working together in the classroom.

"If effectively managed, they will bring about major changes in the culture of schools and in the way staff are deployed and in their roles and relationships. There are real opportunities for reform of the teachers' contract to tackle the workload issue.

"We welcome the proposed limits on teachers' working hours, cuts in bureaucracy and the guaranteed time for planning, preparation and assessment.

"Workload issues are crucial and teachers must be freed to teach and spend time preparing high quality lessons for pupils. Developing support staff roles is necessary to meet these aims, so we welcome the proposed increase in the use of support staff, although they must support - not replace - teachers.

"PAT is committed to a 'whole school team' approach and supports the concept of a fully integrated staffing framework within schools.

"PAT is calling for a proper career and pay structure for support staff, as we believe they are professionals in their own right. Many of those already in post are highly skilled and completing their tasks effectively.

"At present, the roles, deployment, qualifications and training opportunities for support staff vary enormously between LEAs and often individual schools.

"There needs to be a national career and pay structure for teaching assistants and other support staff or firm government guidance on this. Some LEAs have already taken action towards implementing pay scales for support staff, but many lag behind.

"The training and management of support staff is essential to these proposals. Support staff need dedicated, affordable and accessible training with opportunities for continuing professional development.

"Training is also vital for teachers to build relationships with and work effectively with teaching assistants. Governing bodies and head teachers will require training to manage appointments and ongoing performance management."