The first six months of Ofsted's new inspection regime has seen a near doubling in the proportion of schools judged "inadequate" while the proportion rated "outstanding" has more than halved.
The findings of an analysis by The TES of all school inspections published since September, when the new framework was introduced, and the end of February have been greeted with shock and dismay by heads' leaders.
John Dunford, Association of School and College Leaders (ASCL) general secretary, called for an "urgent and radical review" of Ofsted's inspection framework.
Since its introduction, only 9.2 per cent of schools have been given the watchdog's top rating compared with 19 per cent under the old regime.
The proportion of schools put in special measures or given formal notices to improve has grown from 4 per cent to 7.5 per cent.
Ofsted refused to comment on the findings ahead of the publication of its own statistics next week.
The watchdog has always insisted that its new-style inspections would "raise the bar" on its expectations of schools.
It is also likely to argue that the shift in proportions is partly due to its decision to focus on poorer schools and increase the gap between inspections for schools previously judged "good" or "outstanding" from three to five years.
But The TES has found that schools were inspected before Christmas, in the first wave of the new framework, despite being judged "good" only three years earlier.
Among them was Kelsey Park Sports College, Beckenham, which was given a notice to improve in November. Head Brian Lloyd believes that his school was unfairly penalised for a blip in exam results.
Like many of his fellow heads, he believes the new framework is tying inspectors' hands, preventing them from using their professional judgment. He said he was told by an inspector: "I would like to give you a better grade but I can't."
Mick Brookes, general secretary of heads' union the NAHT, said the idea of the inspections being skewed towards poorer schools did not tally with his experience.
He called for Ofsted to stop revamping the inspection framework. "We've got to stop tinkering with the system and have a measure of school performance over time," he said. "All this nonsense about raising the bar is exactly that - nonsense."
Primary schools had the biggest proportionate increase in "inadequate" verdicts under the new framework, from 3 to 7.3 per cent of reports. Secondaries saw the biggest drop in "outstanding" judgments from 22 to 9.5 per cent.
The issue is likely to feature prominently at ASCL's annual conference in London this weekend, with many members feeling there is an unfair emphasis on raw exam results. Dr Dunford is expected to use his speech on Sunday to say: "Schools and colleges need to be judged in context, not just on data.
"Too often the inspection judgment is little more than an echo of the data, paying little heed to the context. Some feel that the judgments could have been telephoned in beforehand."
A Department for Children, Schools and Families spokesman said that June's 21st century schools white paper had made clear the intention to raise the bar on school inspection. "We expect Ofsted's inspection grades published next week to reflect this," he added.
Original paper headline: `Inadequate' schools double under new Ofsted regime