Estyn has been forced to defend its new inspection framework amid accusations that it is getting tougher on local authorities to suit the education minister's agenda.
Last week, Pembrokeshire council's education service became the second to be rated unsatisfactory by the inspectorate in as many months.
Estyn found "systemic corporate failures" with the council's policies and procedures for safeguarding children, which led to a follow-up investigation with the Care and Social Services Inspectorate Wales.
It also found learners do not perform as expected at the end of key stages 1 and 4 and attendance rates in primary and secondary schools are adequate and have declined over the last four years.
The report said Pembrokeshire's capacity to improve is unsatisfactory and the quality of information that officers share with elected members does not allow them to properly challenge school performance.
However, the council is widely considered one of Wales's leading education authorities and in 2008, during the previous inspection cycle, it received a glowing report from Estyn.
It was even highlighted as a example of good practice in this year's annual report by chief inspector Ann Keane for the quality of its strategic management, based on the strength of the 2008 report.
After last month's damning report on the quality of Blaenau Gwent's education services, which saw the council placed in special measures, some educationalists are beginning to question Estyn's judgments.
Rex Phillips, Wales organiser of teaching union the NASUWT, accused the inspectorate of "pandering" to the agenda of education minister Leighton Andrews.
The minister has made no secret of his desire to improve local authorities' ability to deliver education services, and has threatened wholesale top-down reform if standards do not improve.
Mr Phillips said: "The Pembrokeshire report is a further indication that Estyn is compromising its independence to serve the minister's agenda.
"There's no comparison between this report and that of 2008. Are we expected to believe that in just three years this authority has gone downhill to this extent? If Estyn continues to produce reports of this nature it will further undermine its credibility."
ATL Cymru director Dr Philip Dixon said there had been a "sea change" in Estyn, and it should explain carefully why that was the case.
"These reports have come at a time when the minister has said we have a failing education system that needs to be shaken out of its complacency," he said. "Estyn needs to strive diligently to maintain the confidence of the profession."
Estyn said its new inspection cycle uses a different framework and its judgments are now "more realistic and more focused on outcomes for learners".
It pointed out that local authorities themselves took part in shaping the framework and that inspection teams include a nominee from each authority.
A spokeswoman said: "In the new cycle we are placing a different emphasis on aspects of local-authority performance, particularly the authority's ability to improve outcomes for learners and the impact of its services in challenging, supporting and intervening in the work of its schools."
Each local-authority inspection starts with an analysis of its outcome data and self-evaluation reports.
"If the analysis reveals low or declining standards and the self- evaluation fails to recognise this or address it convincingly then judgments will be critical," the spokeswoman added.
Pembrokeshire is the seventh council inspected under Estyn's new framework. So far, Conwy and Neath Port Talbot have been rated good, Cardiff, Wrexham and Powys adequate, and Blaenau Gwent and Pembrokeshire unsatisfactory. None has been deemed excellent.
70 days to show action plan
Pembrokeshire must now undertake a "rigorous" evaluation of all safeguarding work within its education department and schools, and improve school standards and attendance.
It must produce an action plan within 70 days, showing how it will address the recommendations, and it will face re-inspection by Estyn.
The council said safeguarding children was a priority and it would not hide from the issues raised. It said it is already addressing many of the educational concerns.
The Welsh Government called the findings "wholly unacceptable" and said the education minister would consider the decline in school standards and other issues about education services, and expects to see the council's action within two months.
Original headline: Unions claim Estyn's tough new approach `panders' to minister