Around 150 pupils at The James Hornsby high school in Laindon, near Basildon, Essex, now face a further wait before discovering their full results.
The examinations officer, drama teacher Gillian Hearsey, was said to have been suffering "health problems" when she failed to post the papers.
An Essex local education authority spokesman said she would be the subject of a disciplinary inquiry by governors and could be dismissed.
The problem emerged last week after examination boards repeatedly complained they had not received all of the school's papers.
Headteacher Jacqueline White confronted the teacher, who said a number of papers, thought to be around 300, were locked in a cupboard.
Examiners from four different boards are now marking the scripts, which included GCSE papers in mathematics, science, English and design and technology. The school hopes pupils will get their results within the next two weeks.
George Turnbull of the giant Assessment and Qualifications Alliance exam board said nothing like this had happened before.