The anti-agreement NUT must explain why it continues to oppose a deal which has the support of almost two-thirds of the profession and half of its own members.
Meanwhile, ministers are left crossing their fingers that support for the agreement will hold, despite the slow pace of change on the ground. Also, the finding that an overwhleming majority of teachers oppose teaching assistants taking lessons does not augur well for later stages of the agreement that guarantees time for marking and lesson preparation and covering for absent staff.
Support for the agreement is higher among secondary teachers (68 per cent) than primary (56 per cent), and in Wales (73 per cent) than in England (62 per cent) - especially London and the South-east (57 per cent).
More experienced staff are also more likely to support the agreement than those new to the profession. But there is evidence that teachers' views are shaped by their union's position on the agreement.
About three-quarters of the pro-agreement National Association of Schoolmasters Union of Women Teachers (NASUWT) and Association of Teachers and Lecturers (ATL) members support the deal. This pattern is repeated in teachers' views on assistants taking classes.
NUT members, most of whom are primary teachers, are again the most hostile: 88 per cent oppose assistants taking classes in the absence of a teacher; but in this case they are joined by a majority from the ATL (73 per cent) and NASUWT (82 per cent).
Ministers argue that without allowing assistants to cover for absent teachers there is no way of reducing the burden on teachers. They also envisage higher-level assistants taking some classes on a regular basis.
But with 83 per cent of primary and secondary teachers against the move, the Government must fear that implementation of the agreement will be difficult.
Opposition to assistants taking classes remains even if this were to reduce teachers' workload.
Two-thirds oppose assistants covering for short-term absences even if it reduces teacher workload and almost three-quarters are against assistants supervising classes to allow teachers time for planning and marking.
John Bangs, the NUT's head of education, said: "All teachers would be in favour of a workload agreement.
"But what we have got is a workload and remodelling agreement which has the potential to undermine teachers' professional status."