Ofsted inspectors have branded a Northamptonshire school set to become an academy as "inadequate".
Northamptonshire County Council wants to turn Weston Favell School, which is in special measures, into an academy to tackle its "under performance".
In an Ofsted report inspectors said there was "very little improvement" in students' progress.
Teachers at the school went on strike in opposition to the academy plans on 3 December.
They argued the school should continue to be run by the local authority.
A new headteacher has been in post since the start of the summer term.
The report said: "The progress lower attaining students make remains a concern largely because there has been limited progress in addressing major shortcomings in the provision for students with special educational needs and/or disabilities."