It must be particularly galling for the 69 per cent of respondents to Bernard Lamb's questionnaire who thought grammar should be taught as mistakes crop up in pupils' work, or the one in four comprehensive school teachers Mr Lamb claims fail to correct even basic errors.
Poor spelling and missing punctuation were among the "absolutely unforgivable" sins picked out by Dr Lamb, a biologist, in his third survey for the Queen's English Society, launched to coincide with its conference on Saturday.
"Some of them couldn't even spell grammar," he said. "There were elementary mistakes that they would have been told off for in primary school."
Dr Lamb previously carried out surveys of English standards among undergraduates and recruits to industry and commerce.
Some 550 teachers from comprehensive, grant-maintained and independent schools and further education colleges responded to the latest survey.
They were asked about standards of pupils arriving and leaving their institution, about the teaching styles they were encouraged to adopt and which mistakes they corrected in pupils' work.
One in five secondary teachers said pupils arrived with poor English standards. But among FE teachers the figure rose to 36 per cent.
Younger staff tended to correct only half as many mistakes "probably because of indoctrination at teaching college," Dr Lamb said. "Standards cannot help but get worse because pupils will never be told when they are wrong."
That interpretation was echoed by some speakers at Saturday's conference, who called for more formal training in the teaching of English and grammar at teacher training colleges.
Dr Lamb believes the argument is already being won with the Teacher Training Association's introduction of a more detailed curriculum in training courses.
He was alarmed that only 28 per cent believed grammar should be taught explicitly (53 per cent taught it in this way).
Just 6 per cent of teachers said they were discouraged from using whole-class teaching and only 2 per cent were discouraged from correcting punctuation, spelling or grammar errors, 80 per cent taught punctuation explicitly.
One teacher thought Latin should be brought back. Another thought grammar was "boring and irrelevant" (and made seven errors in 15 lines - "should not be teaching English," Dr Lamb sniffed). Most views fell somewhere between.