More than a quarter-of-a-million children are being taught at under-performing secondary schools, according to official figures.
The data suggests that 11.6% of state-funded mainstream schools, 346 in total, fell below the Government’s minimum standards in 2018.
According to Press Association analysis of the data, it means 282,603 schoolchildren are now being taught at under-performing secondaries – about 9.3%.
Schools fall below the Government’s performance threshold if pupils fail to make enough progress across eight subjects, with particular weight given to English and maths.
In 2017, 365 schools fell below the floor standard, but the figures are not directly comparable.
This is because the latest data does not apply to University Technical Colleges (UTCs) or further education colleges with 14-16 provision or studio schools.
School leaders said performance tables are “long past their sell-by date”, urging the public to take into consideration the data used to compile them.
Geoff Barton, general secretary of the Association of School and College Leaders, said: “Performance tables can never tell the full story of a school and we urge parents and governors not to place too much weight on them.
“The secondary school performance tables are inherently flawed in that the headline measure of Progress 8 which is used to judge the performance of schools effectively penalises schools which have a high proportion of disadvantaged children.
“The effect of this is to stigmatise these schools, making it more difficult to recruit headteachers and teachers and demoralising pupils, parents and communities.”
He added: “Current performance tables are long past their sell-by date.
“We urgently need fairer performance measures which better recognise the achievements of schools that teach the most vulnerable pupils.”
A secondary is considered to be below the Government’s floor standard if, on average, pupils score half a grade less (-0.5) across eight GCSEs than they would have been expected to compared to pupils of similar abilities nationally.
Thursday’s data, which covers every secondary in England, shows Yorkshire and Humber has the lowest proportion of under-performing schools, while the North West has the highest.
The figures also show the proportion of pupils achieving a grade 5 or above at GCSE in both English and maths has increased, from 42.6% last year to 43.3% this year.
The attainment gap between disadvantaged pupils and others increased slightly, rising by 0.6% between 2017 and 2018.
The Department for Education data further reveals that 95.5% of pupils are now entering EBacc science at GCSE, up from 63.2% in 2010.
Andy Ratcliffe, CEO of education charity Impetus-PEF, said: “Today’s figures show that disadvantaged young people continue to be significantly less likely to achieve crucial GCSEs in English and maths than their better off peers.
“The gap between the two has in fact widened this year.
“English and maths are essential for young people to progress to the next stage in education or into work, and we know that young people who don’t achieve the grades by 16 are unlikely to catch up.”
School standards minister Nick Gibb said: “Making sure that all pupils, regardless of their background, are able to fulfil their potential is one of this Government’s key priorities and these results show that more pupils across the country are doing just that.
“It’s been clear for some time that standards are rising in our schools and today’s data underlines the role academies and free schools are playing in that improvement, with progress above the national average and impressive outcomes for disadvantaged pupils.”