An examiner's bag containing 32 O-level Additional Mathematics Paper 2 scripts from Singapore was taken by mistake by a train passenger in Britain in November last year.
The scripts, which make up 56 per cent of the subject grade, have not been found despite a major investigation by Cambridge Assessment - which administers the examination and marks the scripts. The bag was lost in transit from London to Sheffield in England on Nov 21.
This comes about a year after a parcel containing A-level Chemistry answer scripts from 238 Singapore students was stolen from a courier van transporting it to an examiner in Britain in November 2017.
The Singapore Examinations and Assessment Board (SEAB), which briefed the media yesterday, said the scripts in the latest case were from two schools - 20 from Nan Hua High School and 12 from Hong Kah Secondary School, which is now known as Jurongville Secondary.
The students, who received their O-level scores yesterday with the rest of their cohort, have been awarded final grades for Additional Mathematics based on their performance in Paper 1 and their cohort's performance in both papers.
Their marks in Paper 1 were used to work out their position in terms of percentile ranking within the cohort. The ranking was then used to derive the missing Paper 2 marks. To ensure consistency, their school preliminary exam results were also taken into account.
About 91 per cent of the affected candidates, or 29 of them, obtained at least a pass grade, with about 20 getting distinctions - A1 or A2. SEAB said almost all affected candidates had better or the same grades for the subject, compared with their school preliminary exams.
Its chief executive Tan Lay Choo said: "We were very upset, disappointed and also shocked that it happened so soon after the first incident... We want to give them a grade that is fair and valid ."
SEAB will be meeting Cambridge Assessment in about two weeks in Britain to discuss how to improve processes. "We'll also be looking into whether there is cause for us to seek penalty," Ms Tan said.
As in the first case, the students can opt to retake the paper on Feb 15. The better of their two grades - the awarded grade or the one from the second exam - will be counted. They have until Friday to make their decision.
Nan Hua High School principal Tan Jong Lek said the school is confident the students have received a fair and valid assessment, adding that the students "accepted the news calmly". A very experienced teacher will help those who opt for re-examination.
Jurongville Secondary School principal Chan Yew Wooi said the affected students' teacher will set aside every Friday afternoon to meet those who need assistance in their preparations for the re-examination.
Cambridge Assessment's director of assessment Juliet Wilson, who was at the briefing, said Cambridge Assessment started an extensive search through rail companies and the police. It notified SEAB on Dec 14 after it became certain that the scripts were unlikely to be found.
The bag was in a luggage rack near the door of a train carriage and was mistakenly taken by another passenger as it looked like his. The examiner will not be engaged in future as he has breached the security policy by leaving the scripts unattended.
Mrs Wilson said scripts are sent to examiners who are from across the country. "This is a really unfortunate incident, and I have come (here) to show you... how sorry Cambridge Assessment is."