Canadian firm linked to last year’s grading errors will not be involved

Vast majority of students have formally applied for exams, accredited grades or both

‘In any scientific process, a correct result is produced through trial and error,’ says Polymetrika chief

Disclosure prompts calls for a full inquiry to establish if there are further errors

About 6,500 students awarded grades lower than they should have received, says Minister

Department of Education made payment to Canadian company without tendering process