The report focuses on a new regime introduced in 2005
The short, sharp Ofsted inspections present a "superficial snapshot" of England's schools and rely too much on test and exam results, a report claims.
The report by the think tank Civitas says poorly trained inspectors take a "tick-box" approach to gauging quality.
Civitas says Ofsted reports - used by many parents to judge schools - do not give a "well-rounded picture".
Ofsted denies relying on test results, and says it considers other evidence, including the observation of lessons.
The Civitas report is a collection of essays by nine authors, among them a practising inspector, two head teachers, a parent and a former chief inspector.
Anastacia De Waal from Civitas says she believes there is 'misplaced confidence' in Ofsted
They focus on the new "light touch" regime introduced in 2005.
Whereas in the past a school could have up to 18 inspectors visiting over four or five days, under the new system this has been reduced to a maximum of five over two days, it points out.
One contributor, serving inspector Sarah Drake, said there were some advantages to the new system including a more collaborative approach using schools' self evaluation materials, less disruption for teachers and more frequent inspections.
But other elements were less successful, including the tightness of the schedule which could make work difficult and limited the number of lesson observations.
"There is a real time shortage for inspectors with the new inspection regime. Thoroughness is imperative for sound inspection judgements," she said.
She also noted: "Delays in getting validated statistical data about Sats, GCSE and other test results mean that what we are using can be up to 16 to 18 months out of date."
Times Educational Supplement reporter Warwick Mansell highlighted that of the 6,331 primaries visited in 2006-7, 98% had the same inspection verdict overall as they had for "achievement and standards" - which is based on test results.
Many educational practitioners feel that the inspectors' minds are made up long before they observe the quality of teaching
Barry Sheerman MP Chairman of the Commons children, schools and family committee
The shortened and short-staffed nature of today's inspections had left inspectors unable to properly investigate whether this performance data was reliable, the report said.
Barry Sheerman MP, who chairs the Commons children, schools and families select committee, said accountability was necessary but many people feared that "teaching to the test" can prevent pupils from getting a full education.
He added: "Many people believe that more attention should be paid to inspection reports than to the results of GCSE and A level results - yet, as inspection reports and results become more interchangeable, many educational practitioners feel that the inspectors' minds are made up long before they observe the quality of teaching or the atmosphere within the school."
Former chief inspector Pauline Perry questioned whether the Ofsted approach had done enough to raise the bar for the lowest achieving schools and disadvantaged pupils.
She argued that it had not and said the gap between the most disadvantaged and the highest achieving has widened.
"Ofsted has not succeeded in becoming the force for educational achievement that successive governments had hoped," she concluded.
Anastasia de Waal, head of education and family at Civitas, said criticism of Ofsted was nothing new but despite its new approach, it was still considered "unnecessarily punitive".
Ofsted said Civitas appeared not to understand how inspection worked.
In a statement, it said: "Ofsted considers the progress learners make in the school, the background of its pupils, the school's own self-evaluation and evidence from the direct observation of lessons.
"All this evidence enables school inspectors to make more than 30 judgements including safeguarding, equalities, behaviour, teaching and the effectiveness of leadership and management.
"Only one judgement relates directly to exam or test results."
Ofsted said its own post-inspection research found 96% of headteachers thought the right issues for improvement had been identified.
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