Hundreds of teachers are struggling with spelling, numeracy and the basics of their subjects, reports by school inspectors suggest.
Analysis of Ofsted ratings shows many make mistakes during lessons or when marking work, leaving children confused.
In some examples uncovered by the Mail, teachers were actually inserting errors into pupils' work.
Other cases involved teachers displaying 'weak subject knowledge' and offering 'muddled and confusing explanations'.
The findings show most mistakes are taking place at primaries, when children are learning the basics of core subjects such as English, maths and science.
Campaigners say it suggests some teachers themselves are so poorly educated they are passing on their mistakes to youngsters.
The findings come from analysis of 280 schools inspected by Ofsted over the past few years and graded 'inadequate' for teaching.
At least 22 were identified as having teachers who lack basic literacy and numeracy skills, or knowledge of the curriculum.
In one example from last year, inspectors at Dines Green Primary in Worcester found that 'teachers make mistakes when teaching English and mathematics which leads to pupils becoming confused'.
At Wilkes Green Infant School in Handsworth, Birmingham, a teacher 'used incorrect grammar in their written feedback to pupils about their work' in 2016.
This year at Dormers Wells Infants in Southall, west London, teachers had 'weak subject knowledge' which led to 'misconceptions in pupils'.
Last year at Central CE Academy in Chichester, West Sussex, inspectors noted 'sometimes adults unintentionally introduce errors into pupils' work, including spelling'.
And also last year at Edenbridge Primary in Kent, Ofsted said: 'Some teachers' subject knowledge is poor. At times, they offer pupils muddled and confusing explanations of concepts in mathematics and English grammar'.
Chris McGovern, of the Campaign for Real Education, said: 'Many teachers too were failed by their schooling. They are incapable of providing the next generation with basic skills and core knowledge.
'We are the only country in the developed world where grandparents out-perform their grandchild.'
When approached for comment, many of the schools said they now have new leadership teams which have made improvements since the inspections were carried out.
School standards minister Nick Gibb said: 'We are confident in the quality of our teachers and their teaching. As part of initial teacher training, all teachers must pass tests in numeracy and literacy to achieve qualified teacher status.'
Children who have books at home are three times as likely to have good reading skills than those who don't, a study found.
The National Literacy Trust found reading for pleasure at home, particularly at pre-school age, gives children a head start, with 12 per cent who had books at home reading above their age level, compared with just 4 per cent who had none.