Teachers’ shaky grasp of grammar and punctuation has been exposed in a survey of the nation’s literacy skills.
Two-thirds made a basic apostrophe mistake in a test administered to more than 2,000 workers from key professions. Eight per cent even muddled the use of I and me.
Teachers made a string of blunders despite being responsible for drumming correct English into the next generation.
Their less-than-polished performance left them lagging behind employees in the creative and arts sectors.
They managed only to match financial workers, who are hardly known for their strong literacy skills.
Among other errors, teachers slipped up on the correct use of apostrophes, with many making the classic "greengrocer’s" error.
Plural nouns in English do not have an apostrophe – as in "newspapers" – but the rule is often broken.
Shopkeepers sometimes advertise apple’s and pear’s for sale, hence the term greengrocer’s apostrophe.
In the punctuation test, two thirds wrongly tried to place an apostrophe before or after the "s" in the sentence "The 70s was a great decade for music".
Nearly half failed to use the apostrophe correctly in "The Smiths’ house is a disused windmill".
Another exercise required workers to choose the correct word in the sentence "I implied/inferred/ensued from his art collection that he was extremely wealthy".
Seven per cent wrongly picked "implied" while a similar proportion believed the answer was "ensued".
Eleven per cent thought it was "none of the above" while seven per cent passed on the question altogether.
Some eight per cent failed to give the correct answer to a question requiring respondents to choose between "I" and "me".
The findings prompted recruitment agency Kelly Services, which conducted the online test, to declare that teachers were not the "grammar gurus" they claimed to be.
The snapshot survey appears to reinforce concerns arising from the stubbornly-high failure rate for official literacy and numeracy tests given to trainee teachers.
The tests were introduced to drive up the calibre of the workforce but results show that one in five still has problems with spelling, punctuation and simple maths after spending at least 16 years in education.
Meanwhile Ofsted has reported that teachers who struggle with spelling are behind a litany of mistakes in pupils’ work.
They fail to correct glaring errors which even the pupils later spot, leaving the children confused about what is correct.
Teachers’ literacy weaknesses are thought to stem from the prevalence of "trendy" classroom methods in the 60s and 70s.
Today’s crop of teachers were not given a good enough grounding by their own schools, which failed to put enough emphasis on the three Rs.
Steve Girdler, a director at Kelly Services, said: "The research bore out our suspicions about the UK’s poor levels of competency in grammar.
"A logical solution would be to send people back to school, but closer inspection of the results revealed teachers were far from the grammar gurus they claimed to be."
A spokesman for the National Union of Teachers pointed out that teachers were far from being bottom of the class in the online test, adding: "It would be nice to eliminate the problem completely but teachers are human beings and subject to error."