Fewer than half of secondary teachers believe that teaching assistants help reduce their workload, a government-backed study has found.
Widespread scepticism about the skills and deployment of support staff exists in both primary and secondary schools, according to the survey by Birmingham university.
The findings will be seized on by critics of the Government's workload reform as a key part of the deal is to employ more support staff to help teachers.
Only 45 per cent of secondary teachers said that working with teaching assistants reduced their workload. One in seven strongly or very strongly disagreed. That compares with three-quarters of primary and two-thirds of special school teachers who said that assistants helped them.
Professor Hywel Thomas, one of the authors of the report, said the difference of opinion may be down to the fact that there are more assistants in primaries.
"Secondary teachers have less experience of working with teaching assistants and it may be harder for them to see the benefits," he said.
But John Bangs, National Union of Teachers' head of education, said: "It is inevitable that managing assistants will mean that the workload for a large number of teachers does not fall and may even increase.
"It is typical of the Government's approach that it only gathered this evidence after it decided its policy."
Professor Thomas's team questioned more than 1,300 teachers in all the primary, secondary and special schools participating in the Government's pathfinder workload reduction pilots. Three-quarters of secondary and half of primary teachers said that support staff were underused by schools.
Seventy per cent of all teachers believed that "teaching assistants need more training".
From this term, more than 20 clerical and administrative tasks will be transferred to support staff.
By September 2005, every teacher will be given guaranteed planning, preparation and assessment time equivalent to 10 per cent of their teaching hours.
Teachers in the pilot schools supported both measures but also wanted smaller classes, fewer government initiatives and the employment of more qualified staff. The survey was carried out in April and May last year, before measures to reduce workload in the schools were put in place.
A follow-up survey carried out in April and May 2003 is currently being analysed.
Analysis 26 'Modernising the school workforce: initial perspectives' by Professor Hywel Thomas, Celia Brown, Dr Graham Butt, Dr Helen Gunter, Ann Lance and Dr Steve Rayner of the University of Birmingham