Two multi-million pound academies have been described as inadequate by Ofsted in the same week.
Sheffield Springs Academy and Westminster Academy have both been heavily criticised by inspectors for failing to reach high enough standards and have had their overall performance given a grade four - the lowest possible mark. The schools have each been issued with a notice to improve.
Sheffield Springs, sponsored by Christian charity the United Learning Trust (ULT), was visited by Gordon Brown in May, just one week before inspectors called.
The Prime Minister praised the school's pupils for their "dynamism", "determination to succeed" and "high morale".
But inspectors found a catalogue of problems, including teachers failing to meet students' individual needs, poor leadership and inadequate governance.
The school was described as transforming "the climate for learning" when it first opened to pupils in September 2006, but over the past year it was found to have suffered a "loss of impetus stemming from a lack of strategic leadership and the failure to tackle key weaknesses". "This has led to a breakdown in relationships at a senior level," the report said.
ULT, the country's biggest academy sponsor, has been criticised before for problems with school leadership.
Serious concerns have been raised that more than half of the principals at its schools have been replaced within two years of the chain's 15 academies opening.
The sponsor has now drafted in Kathy August, its director of school improvement and executive director of Manchester Academy, to get Sheffield Springs back on track.
"ULT takes full responsibility for the outcome of this inspection and accepts the Ofsted report in full," a spokesman for the charity said.
"While important progress has been made since the academy opened, it is evident that much more needs to be done. We are determined to accelerate the progress underway and staff at the academy share this determination."
Its sister school, Sheffield Park Academy, which is also sponsored by ULT and being assisted by Ms August, was inspected at the beginning of this month. The official report has yet to be published, but fears have been expressed locally that it will also be criticised.
Westminster Academy in west London, which also opened in September 2006, was criticised for poor standards of attainment.
Although the school started from an "exceptionally low base" of exam results, too few pupils were making sufficient progress, inspectors warned. But Ofsted praised the school for establishing a positive culture and noted that "students sought out inspectors to say how proud they are of their academy and that they enjoy their time there".
Sixth-form provision was also praised following the introduction of the international baccalaureate, which inspectors said showed the school's capacity to improve.
John Bangs, of the NUT, said: "A notice to improve is something that no school wants and these examples dispel the illusion that academy status gives some kind of magic protection. The sooner ministers stop thinking that academies are the cure to problems in schools in tough areas, the better."