The exam they sit, however, is the global equivalent of the GCE O levels, called the International General Certificate of Secondary Education (IGCSE).
So why do they do this, when the IP allows them to bypass the O levels to finish with A-level qualifications?
BACKGROUND STORY
Sole option
'If she were to leave after Sec 4, she would have had only her PSLE certificate. The IGCSE is recognised internationally, so she took that.'
A FATHER, on his daughter who took the IGCSE in 2009
Some want to know where they stand; others are simply interested in the subjects.
Still others hope, after Secondary 4, to apply to American universities, which recognise IGCSE grades.
Most importantly, these students want a 'safety net': Should they not fare well in the A levels, they would only have their Primary School Leaving Examination (PSLE) certificate and their secondary school grade point average to fall back on.
The British Council, which administers the IGCSE for private candidates here, said 69 students took it last year. Six in 10 were Singaporeans, mostly between the ages of nine and 20.
The British Council said it neither has figures for previous years nor tracks the schools these candidates were from.
The IGCSE is offered by several exam boards in England. One of them is Cambridge International Examinations, which said that, since 2008, more than 16,000 candidates from Singapore, mostly from the international schools, have sat the exam.
The number has grown, on average, by 19 per cent a year.
Another board, Edexcel, said that about 1,100 students from here sat the exam last year, 20 per cent of them as private candidates.
Students in government, government-aided or independent schools are barred from registering as private candidates for the GCE O levels taken by Secondary 4 and 5 non-IP students. This is why IP students end up taking the IGCSE.
Schools offering the IP, such as Raffles Institution (RI) and Anglo-Chinese School (Independent), declined comment, saying they do not track students who sit the IGCSE; a spokesman from Hwa Chong Institution (HCI) said it had no knowledge of any of its students taking it.
ACS(I) student Fareed Muhammed Noorul Amin, 15 and in Secondary 3 of his school's IP, said that when he sat the IGCSE last year, several students from HCI and RI were in the exam room with him.
He is due to finish his six years at ACS(I) with an International Baccalaureate diploma in 2015.
He said he had enquired about taking the GCE O-level exam as a private candidate but was barred because he was enrolled in ACS(I), an independent school.
He took the IGCSE instead, going for two mathematics and two science subjects, and throwing in geography and English 'for a complete certificate'.
He scored five A* and an A for the six subjects.
Interest in the subjects aside, he said the exam gave him 'a good gauge of how well I fare in the respective subjects'.
He is thinking of sitting the A levels soon.
He has the support of his housewife mother Mehar Banu, 35, and engineer father Noorul Amin Alawdeen, 42.
Mr Noorul said: 'He has always been interested in mathematics, so I thought it would be good if he had a full certificate. Taking the exam also improves his knowledge.'
An alumnus of RI, who declined to be named, took the IGCSE several years ago to get a 'safety net', in case he did not ace the A levels.
But he did well enough, and is now in an American university.
One father, who declined to be named, said his daughter, who was also in RI's IP, took the IGCSE in late 2009. It was the only option for her as she wanted to study in the United States after Secondary 4.
He said: 'If she were to leave after Secondary 4, she would have had only her PSLE certificate. The IGCSE is recognised internationally, so she took that.'
