They accused Ofsted and Chris Woodhead, its head, of forcing thousands of talented inspectors out of the system by squeezing budgets and increasing work. They told MPs schools were not getting the high-quality service they needed to raise standards.
Geoff Penzer, director of one of the leading agencies supplying school inspectors, said in a submission that Ofsted's policies "are leading to a haemorrhage of many of the best inspectors and a general 'dumbing down' of the inspection process."
Individual inspectors also joined the attack, accusing Ofsted of halving the budget for inspections, forcing thousands of the best staff out.
The Commons Education Select Committee heard inspection teams often had to meet in their hotel the night before visiting a school to discuss their work. In most cases, pressure of work meant inspectors could spare only five minutes to give a teacher feedback.
Inspectors and contractors said scrutiny of schools had increased since Ofsted was created but that could be lost because experienced staff were leaving for better-paid work.
Inspectors are all freelance or agency staff who bid for Ofsted contracts to produce school reports. The pay of registered inspectors, who lead Ofsted teams, has been cut from pounds 5,000 per report to pounds 2,500, inspectors say. But individual team members can get as little as pounds 160 for each day they spend in a school, which covers expenses and "writing-up" time as well as the school visit itself.
A survey by the Institute of Registered Inspectors of Schools found nearly 80 per cent thought pay rates were too low and "endanger the quality of inspections". Fifty-five per cent said the system of checking the quality of inspection reports was unsatisfactory.