How are PSLE Aggregate Scores calculated?

To understand how PSLE Aggregate Scores are calculated, we must first understand T-Score. T-Score is the adjusted score a student will get for a subject, after a series of tabulations has been made.

Formula for T-Score


X = Raw score of student
Y = Average Score of the whole cohort
Z = Standard Deviation* (SD)

Standard Deviation* (SD) is the spread of the marks around the average.

Example 1 -
Allan, Bernard and Charles have $45, $50 and $55 respectively. They have an average of $50 each.

Example 2 -
Dan, Edward and Frank have $10, $50 and $90 respectively. They also have an average of $50 each.

In Example 1, the spread ($45 to average of $50 and $55 to average of $50) is smaller than the spread in Example 2, where the spread is bigger ($10 to average of $50 and $90 to average of $50)

As such, Example 1 will have a smaller SD, as compared to Example 2.


Simpler Way to read Standard Deviation (SD)

If the average score of 3000 pupils who sat for Science Test is 50 marks and the SD is 5, it means that 2/3 of the 3000 pupils have scored 5 marks around the average, which means 2000 of the students scored from 45 to 55 marks.

If the average score of the same 3000 pupils who sat for Mathematics Test is 50 marks and the SD is now 10, it means that 2/3 of the 3000 pupils have scored 10 marks around the average, which means 2000 students scored from 40 to 60 marks.


Example of how T-score is calculated

Li Ting’s score for Mathematics – 90 (X)
Average score of cohort – 75 (Y)
Standard Deviation - 20 (Z) (this means 2/3 of cohort scored from 55 to 95)

Using the T-Score formula

T = 50 + 10(X – Y) / Z

T = 50 + 10 x (90 – 75) / 20

= 50 + 10 x 15/20

= 50 + 10 x 0.75

= 57.5

Li Ting’s T-score for Mathematics is 57.5