More than 30 academies have been warned they must pull their socks up - or their sponsor could face the sack, the Government disclosed today.
Figures show 34 academies were issued with "pre-warning" letters - demanding urgent action to improve their performance or face being issued with a formal warning as a prelude to losing their sponsor if they fail to heed it.
In six cases, sponsors have been sacked and replaced in a sign that ministers do not intend to give their academies an "easy ride".
The 34 are the first to be given warning notices - none was issued during Labour's term of office. Since the Coalition Government took office, the number of academies has expanded from just 203 to 3,416.
A spokesman for the Department for Education said that "results in a minority of sponsored academies remain stubbornly low", "We will not tolerate long-term under-performance in any school - including in an academy," he added.
He added: "If these academies still do not make the progress we expect, we will take further action. This may result in a change to the sponsorship arrangements."
In the case of a sponsor with a chain of academies, it could lead to it being barred from taking on any new projects.
In one case, Thetford Academy in Norfolk, which brought together two schools at the opposite end of a housing estate, there was strong local opposition to the academy and staff and pupils from the two schools were in open conflict when it opened. The original principal and vice-principal quit within the first two terms and GCSE results to just 28 per cent achieving five top grade A* to C grade passes including maths and English.
Education standards watchdog Ofsted found achievement was too low, there was too much inadequate teaching, attendance was persistently low, behaviour was inadequate and attitudes to learning "left much to be desired".
The sponsors - three local colleges - acknowledge they did not have the resources to put things right - and were replaced by the Inspiration Trust who put in Rachel de Souza, a head who had successfully turned the Ormiston Victory Academy, also in Norfolk, round - increasing the GCSE "pass" rate by 30 percentage points in two years.
Department officials say that - in the vast majority of cases - the pre-warning letters have done the trick - with GCSE results improving by an average of 16 percentage points in the eight academies given pre-warning notices in 2011/12. Ministers are expecting a similar increase with most of the rest when this year's individual school results are published in January.
In one case, the John Madejski Academy in Reading, the school had never reached the Government's minimum target of 35 per cent getting five A* to B grades at GCSE including maths and english. A new principal was appointed who oversaw a 12 percentage point increase to 45 per cent this year.