Kent County Council has been ordered by the government to improve its Special Education Needs and Disabilities (SEND) provision.
Claire Coutinho MP, Minister for Children, Families and Wellbeing, issued the Kent authority with an Improvement Notice on Thursday.
The action comes after the government concluded that the authority had failed to make sufficient progress against nine areas of weakness following a joint Ofsted and Care Quality Commission inspection last November.
The council has been ordered to draw up an Accelerated Progress Plan to deliver sustainable improvements in all the nine areas identified.
The leader of Kent County Council, Roger Gough, had previously apologised for the county's shortcomings.
The council has just four weeks to make progress. If by May 12, the government is not satisfied, it has warned it may step in to take direct control of the services.
The minister wants an improvement board established with an independent chairman joined by leaders from across education, health and care services, to monitor progress.
Clear targets must be set and measured at 3, 6, 12 and 18 month intervals.
In particular, KCC has been given six months to ensure its has "a permanent, suitably trained, SEND case work team of sufficient capacity to enable the effective delivery of the Education, Health and Care needs assessments" - a recognition that currently the department is understaffed.
In response, the council said: "This formal Improvement Notice provides a focus for the work we already have under way with our partners in the NHS and the education sector to transform SEND support in Kent following as November's Ofsted report.
"We are confident that this whole-system approach to improvement will make a positive difference to the lives and experiences of children and young people with SEND and their families.
"Our Accelerated Progress Plan will be submitted to the DfE within the next six weeks and will set out how we will make significant improvements in the areas identified by Ofsted within the next year."
"We will be publishing more information about our improvement work in the coming months. However, lots of work is already under way."
The council said it had opened a new SEND Enquiries Hub to help families, schools and professionals with questions about SEND support, assessments, placements and education, health and EHC plans, or to put families in touch with the right caseworker if needed.
The SEND Enquiries Hub is open Monday to Friday from 9am to 5pm.
Families can email email@example.com or call on 03000 419994.
The council said it was working to reduce the backlog of annual reviews, focussing on those that were more than two years overdue.
Since November, 200 plans had been amended and issued, and more than 200 plans ceased as they were no longer needed.
Ofsted first reported the significant weaknesses at KCC four years ago in an inspection in 2019.
It found that children with special needs were facing "unacceptable" waits to have their needs attended to.
Dr Lauren Sullivan is the leader of the Labour Group at KCC. She said: "There is yet no public accountability for these failures from Kent County Council.
"We are concerned that KCC's Conservative leadership fundamentally does not understand why parents feel they need to fight against the system to get the support they feel is needed for their children."
Dr Sullivan also expressed concern that one way KCC might lessen pressure on its service would be to refuse more children an Education, Health and Care Plan (EHCP), although KCC's average of 5% of children with an EHCP is above the national average of 2.8%.
She said: "Fundamentally we are concerned there will be ‘gate-keeping’ to stop people accessing the services they need."
The government recommends 250 children’s cases should be the maximum per case worker, but KCC's officers are currently dealing with more than 520 cases, according to Labour.
Maureen Cleator is the chairman of Kent Unison, which represents most of the case workers.
She said: "We have been raising concerns regarding excessive workloads and a culture where staff feel unsupported.
"Despite the sterling work done by front-line staff, the system is being overwhelmed, which is leading to serious issues for children, young people their families - and the staff that are trying to help them."