Marking errors by Educational Testing Services resulted in 4,100 cases of “false failure”, leading to some staff being prevented from taking up full-time posts.

Many states require staff to pass a certificate before taking up jobs.

“Being falsely failed meant some lost jobs they’d been offered, and remained as long-term (supply) teachers, or had to stay in college,” said Robert Schaeffer, of anti-high-stakes testing group FairTest, who was called as an expert witness by lawyers representing teachers suing ETS. The errors emerged only after outside education officials challenged scores.

The false scores were attributed to overly-harsh marking.

Meanwhile, thousands of students have also received marks that were too low - in America’s college-entrance exam. Last week, it emerged a further 393 students had received incorrect scores - on top of the 4,000 disclosed earlier this month - plunging America’s university admissions system into fresh uncertainty.

The College Board, which sets the test, said the marking mistakes were caused by scripts expanding “due to humidity”, causing machines to misread them. Also this month, it emerged that McGraw-Hill tests given to New York pupils duplicated questions from practice tests.

Thomas Toch, of Washington DC think-tank Education Sector, and author of a report suggesting the testing industry is “buckling under the weight” of high-stakes tests, said the errors demonstrated the need for outside monitoring of testing.