In Harrogate, members of the National Union of Teachers will propose balloting for half-day strikes in opposition to non-teachers taking classes. Assistants will be allowed to teach under supervision as a result of the national workforce agreement which the NUT has refused to sign.

In contrast, members of the National Association of Schoolmasters Union of Women Teachers are expected to pass two motions at its conference in Llandudno praising the union’s continuing support for the agreement.

The NASUWT will receive additional support from the Education Secretary Charles Clarke, who is appearing at its conference and snubbing the NUT for the second year running.

Both unions claim their opposing stances have led to them gaining new members.

Chris Keates, NASUWT deputy general secretary, said NUT members would be depressed that their union was “sniping from the sidelines” and “indulging in empty rhetoric” while others were making a difference.

But Doug McAvoy, NUT’sgeneral secretary, said the union’s position was supported. “There is a lot of anger among delegates at the way the Government is encouraging unqualified people to undertake teaching,” he said.

The NUT will not be repeating its call for a boycott of key stage 3 tests following its failed attempt to launch industrial action last year. But an NASUWT delegation will demand the tests’ abolition against the wishes of its executive.

Both unions will debate plans to change education for 14 to 19-year-olds and the growing threat to schools from far-right groups such as the British National party.

The NUT will discuss the problems of BNP members becoming school governors, while the NASUWT will attempt to change its rules so it can expel party members. The Trades Union Congress has suggested that far-right campaigners are joining unions deliberately to win compensation cases if they are asked to quit.

Both unions will also explore whether changes to school inspections are making teachers’ work more difficult.

The NUT conference will be Mr McAvoy’s last as general secretary. At the moment the four contenders for the post are John Bangs, NUT head of education; Ian Murch from the Campaign for a Democratic and Fighting Union; Martin Powell-Davies, a member of the Socialist party and Steve Sinnot, the current deputy general secretary.