A council's decision "do a Brexit" and leave a controversial school improvement service could affect youngsters' education, a teaching body has warned.
On Wednesday, Neath Port Talbot Council cabinet members voted to pull out of the Education through Regional Working (ERW) programme.
The £139m scheme sees councils pay to be part of a regional school improvement consortia - with Welsh Government officials insisting it raises education standards.
Critics argue the scheme is bureaucratic and money goes to the consortia first rather than directly to schools.
Neath Port Talbot Council's cabinet, who are set to see its ERW membership fees quadruple, insists it has not brought any real benefit to kids in the county and have now voted to leave the scheme next March.
However, that decision has been criticised by the Association of School and College Leaders Cymru (ASCL).
Director Tim Pratt said: "We are concerned about the implications of the decision by Neath Port Talbot to withdraw from the ERW consortium. It leaves a question mark over how schools in in the area will be able to access school improvement services."
“The complexity of the funding model also raises questions over the impact on schools in the wider area covered by the consortium.
"The Welsh government, consortium, and local authority must work together to ensure that schools are able to access the services they need."
This year, Neath Port Talbot Council paid £40,000 to ERW - but that amount will increase to between £160,000 and £170,000 next year.
Councillors say the increased costs risk an impact on jobs.
Ahead, of yesterday's cabinet meeting council leader Rob Jones said the authority had been left with "no choice" but to leave.
It is the first time any council has opted to quit the service, which was set up by the Welsh Government in 2012.
And the development may now force a review of what has been a cornerstone of Welsh education policy for seven years.
The National Education Union Cymru called for a "uniform system" of support for schools across Wales arguing that four consortia with four different ways of working was not working.
David Evans, national secretary of the NEU Cymru said: "The fact that there were significant concerns voiced by the authority and its schools, regarding the value of ERW, is not a surprise.
"We have already written to the minister requesting that there be a review of the support provided to schools. Today’s decision by Neath Port Talbot adds impetus to that request. There is clearly a need for a support service but a suitable viable alternative to the system we now have in place has to be explored as soon as practically possible."
ERW said it would not comment about the development.
The Welsh Government has also been asked for comment.
Previously, a government spokesman said: "Regional working is crucial if we are to raise standards in our school system.
"We all have a responsibility to work across local authority boundaries to enable school to school co-operation and to share best practice on behalf of our young people.
"Anyone choosing to step away and not work in that spirit will be a disappointment to everyone else working hard to maintain and raise education standards across the country.
Although Neath Port Talbot Council said it intends to leave the scheme, it still has the option to change its mind and stay in.
