Shortcomings at Denbighshire education authority have been described as "unacceptable" by education minister Jane Hutt.
It is expected the authority will face more damaging criticism from Estyn
A highly critical report by education watchdog Estyn has found "ineffective" political leadership at the council and failures to address poor performance.
It comes days after a consultants' report criticised standards in schools.
Council leader Rhiannon Hughes said work was already underway to address the issues.
The council also confirmed that Cllr Dewi Owen has vacated his post as lead member for lifelong learning.
Estyn's 35-page report said children's educational performance was below average at the ages of seven, 11 and at 16 when they take their GCSEs.
In 2006, Denbighshire also came 19th of the 22 authorities in Wales for the percentage of students gaining two AS/A levels.
Funding for secondary school pupils was the second lowest in Wales and overall the report said the performance of secondary schools was well below the expected level when compared with other schools in Wales.
The report also criticised leaders at all levels in the authority for not addressing "robustly and comprehensively enough the continual poor performance of schools" over a long period of time.
Education services overall in Denbighshire have "shortcomings in important areas"
The political leadership for education is "ineffective"
No effective planning for improving education
The school improvement strategy does not focus on the key priorities and actions needed to raise standards
The council's attendance strategy has yet to have a positive impact on overall attendance levels
Exclusions had increased over the last three years at a faster rate than in Wales as a whole and Estyn criticised the authority for often not meeting the needs of excluded pupils.
Communication at all levels within the authority, and between it, schools, parents and pupils was attacked in the report.
The authority did not have an effective system of self-evaluation so education could be improved, and it had a poor track record in managing change, Estyn also found.
Education minister Jane Hutt has written to Cllr Hughes to "make clear the seriousness with which I view the conclusions of the report and my expectation that the authority will take urgent action to turn the situation around".
Ms Hutt said the authority had provided her with assurances, but it was "likely" she would intervene if Estyn was not satisfied with action plan to tackle the problems.
Denbighshire council said it had already begun to address some of the issues and had begun to invest £470,000 a year from 2006-07 on to improve attainment at Key Stage level 3.
It also said it had improved partnership working with the social services and tackled leadership problems at schools with the worst under attainment.
Cllr Hughes said the local people could be "assured that the council has the commitment, enthusiasm and the dedication to improve the situation".
"The report confirms what we already know and work is already well underway to strengthen working practices and improve performance," she said.
The Estyn report comes just days after consultants Cambridge Education painted a bleak picture of education in the county after being commissioned by Denbighshire council.