Teachers' union NASUWT has overtaken its arch rival in Wales, according to official membership figures.
NASUWT Cymru claims 16,500 fee-paying members in Wales - compared with 16,146 for the National Union of Teachers Cymru, according to TUC Wales figures up to May 2005.
UCAC, the Welsh-medium teachers' union, has 3,948 full members while the Association of Teachers and Lecturers has 4,480. The ATL has just appointed a new director in Wales to improve services to members and boost recruitment (see right).
Geraint Davies, secretary of NASUWT Cymru, said rising membership in Wales was a tribute to the support provided by the union's full-time staff and its network of branch secretaries.
He felt the union had also benefited from its "vigorous" bilingual policy and its support for the workload agreement, which the NUT and UCAC refused to sign.
"NASUWT prides itself on the quality of service it provides for its members," said Mr Davies.
"We led the way on threshold payments (for experienced teachers) and are currently leading the way on the workforce agreement.
"While some unions in Wales opposed the agreement, we are proud of the stance we have taken. The agreement has seen a vast and long-overdue improvement in teachers' conditions of service."
Wales as a whole recorded a bigger increase in membership than any of NASUWT's English regions, he said. Within Wales, Ceredigion posted the biggest rise - up 24 per cent.
Dr Heledd Hayes, NUT Cymru's education officer, said she believed the union had not updated its membership figures, and that they were rising and higher than the number held by TUC Wales.
She added: "The reaction we've had is that people are very much in favour of our policies.
"The NASUWT accepts people who are not qualified teachers, including classroom assistants. We feel it's better for everyone to belong to an appropriate trade union, so there is no conflict of interest within one union.
"We do work together as unions and we are all on good terms."
Gruff Hughes, UCAC's acting general secretary, said its membership was rising, albeit slightly. Both UCAC and the ATL recruit in the further education sector as well as schools.
He said small numbers of members were also changing from full to part-time membership, as they scaled down their work commitments on nearing retirement.
"Our membership is not limited to those who teach in Welsh - it's those who speak Welsh. Not all Welsh speakers belong to UCAC, although I would like to see them with us."
Membership figures in Wales for the two headteacher unions are not held by TUC Wales.
Brian Rowlands, secretary of the Secondary Heads Association Cymru, said its fee-paying membership had risen to around 680 heads, deputies, and assistant heads working in Wales's secondary schools.
The association is considering a name change to reflect the new leadership role of its members who are not heads, and those who work in colleges. It also recruits school bursars and managers.
He said: "A lot of our members also belong to UCAC because they are in the Welsh-medium sector."
Anna Brychan, director of the National Association of Head Teachers Cymru, said its membership remained relatively stable across Wales, at around 1,500 fee-paying members.
She added: "Recruitment is rising among deputies and assistant heads.
Overall, our membership is pretty stable - it's heartening given the present number of school closures and mergers."