I REFER to the letter, "Why good grades but low PSLE aggregate?" (my paper, Dec 11) by Ms Chow Chai Foon.

We have clarified the matter with Ms Chow, who asked about the computation of the Primary School Leaving Examination aggregate T-score and whether it is possible for a pupil who has done less well in terms of grades to have a higher aggregate T-score.

We have explained to her that while a pupil's grade for each subject indicates how well he has performed in the subject, his T-score indicates how well he has performed relative to his peers in the subject.

The aggregate T-score, which is used for the purpose of posting pupils to a course in secondary school, is the sum of the T-scores of all the subjects.

The calculation of the subject T-score is based on the raw mark obtained by the pupil, the average (mean) mark of the whole cohort taking the subject, and the spread of marks around the average mark (standard deviation).

It is possible for someone who appeared to have done less well in terms of grades to have a higher aggregate T-score. This is because each subject grade has a range of T-scores.

A pupil getting an A* can be at the lower end of the T-score range, while another pupil getting an A can be at the higher end of the range.

Ms Tan Lay Choo
Chief Executive
Singapore Examinations and Assessment Board

For more my paper stories click here.