The British government has ordered an inquiry into the actions of a U.S. company hired to mark more than a million pupils’ exam papers, after schools complained of missed deadlines, shoddy work and inconsistent grading.

Educational Testing Services Europe last year won a five-year contract to mark standardized tests taken by 11- and 14-year-old pupils across England in English, science and mathematics. The company is a subsidiary of Princeton, New Jersey-based ETS Global.

Pupils took the tests in May, and schools were due to receive all the marked papers back early this month. But officials said almost fifth of primary schools had not received the exams by Friday, the last day of the school year for many.

On Friday, ETS said 71 percent of English papers, 93 percent of math papers and 91 percent of science exams were complete. The company apologized “unreservedly” for the delays.

Some educators have also expressed concern about the quality of the grading, which is done by markers _ many of them former teachers _ hired by ETS.

Teachers and principals have used radio phone-ins and the Internet to complain that many exam papers have been poorly or inconsistently marked. One teacher from northern England released two papers from the same class. One, littered with grammar and spelling mistakes, had been awarded a higher mark than another that was much better written.

Schools Secretary Ed Balls has called the problems unacceptable.

The government has announced an independent review into the delays, due to report in the fall.

Michael Gove, education spokesman for the opposition Conservative Party, accused ETS of “serial incompetence.”

“ETS have forfeited the right to run future SATs tests,” he said.