Mr Woodhead caused a storm of protest from teachers last year when he said there were 15,000 bad teachers, about 4 per cent of the profession.
But figures sent by Mr Woodhead to Don Foster, Liberal Democrat education spokesman, suggest the number is a huge exaggeration. Under the new inspection system demanded by the Prime Minister, under which bad teachers must be reported to heads, the percentage of lessons given the bottom grade was zero and the proportion given the grade next to the bottom was only 1 per cent.
As it is rare for a teacher to get the same grade for every lesson, the figure for bad teachers is clearly less than 1 per cent.
The figures will give ammunition to Mr Woodhead's critics, who say his campaign to raise standards and attack trendy teaching have undermined the profession's morale. Others will say John Major's new system has backfired, because inspectors are reluctant to give the lowest grades now that they are required to report teachers. The inspection results also show Mr Woodhead, whose annual report is due out next week, under-estimated the number of good teachers. He put their number at only three times the figure for bad ones. Although his letter gives only the proportion of good lessons, not good teachers, the difference is clearly greater. Twelve per cent of lessons have been awarded the top two grades.
Overall, the proportion of unsatisfactory lessons between 1 April last year and 17 January was 13 per cent, well down on the 20 per cent given in Mr Woodhead's last annual report.
The new figures grade teachers on a scale of 1 (excellent), 2 (very good), 3 (good), 4 (satisfactory), 5 (less than satisfactory), 6 (poor), 7 (very poor). Under the new system, inspectors from Mr Woodhead's Office For Standards in Education grade teachers. For the first time they are required to report the best and worst (grades 6 and 7) to headteachers. Mr Woodhead's letter suggests most teachers bunch together at grades 3 and 4, accounting for 75 per cent of all lessons. He told Mr Foster it was not possible to give the proportion of bad and good teachers.
Mr Foster said: "Mr Woodhead has a lot of explaining to do. This seriously calls into question his statement of a year ago that there are 15,000 poor teachers. On the face of it, this is a welcome boost for the teaching profession. Given that it was possible to calculate the original 15,000 figure, it is important that he does the same analysis again and publishes the figures."
The reason for the discrepancy between the sets of figures is not clear. Headteachers have complained that inspectors are reluctant to jeopardise teachers' careers by awarding the bottom grades. Right-wingers have also complained inspectors are still not tough enough on teachers.
An Ofsted spokeswoman said: "Mr Foster has confused lesson grades with judgements on teachers. The reduction in the number of lessons graded poor is from 2 per cent to 1 per cent. There are a number of reasons for this. We are currently analysing data concerning the number of very poor and very good teachers identified in the new reporting arrangements."Reuse content