More flexibility - that is what some parents, especially those with children studying overseas, are looking for when it comes to national service (NS).

Pastor Richard Tan, who has been living in New Zealand and Australia for about 14 years, is one such parent.

His son Nathaniel, who is turning 14 and studying in a high school in Perth, left Singapore when he was nine months old.

While making it clear that his son wants to serve NS, and will adhere to any call-up, Mr Tan, 50, prefers that the teenager be allowed to finish his university studies first, so as "not to lose momentum".

He said: "Instead of being disruptive, why can't we extend deferment?"

Under current rules, the Defence Ministry allows servicemen who have gained admission to study medicine at a local university and those awarded the Public Service Commission (PSC) Overseas Merit Scholarship (OMS) to be granted deferment from their NS to pursue their university studies first.

Deferments are also considered for those with "exceptional talent", Defence Minister Ng Eng Hen said in a media interview last year.

This includes the likes of national swimmers Joseph Schooling and Quah Zheng Wen, who are seen as potential Olympic medallists.

Full-time national serviceman Samuel Lim, a 25-year-old PSC OMS scholar, disrupted his NS in 2010 to study public policy at The Fels Institute at the University of Pennsylvania before returning two years ago.

He said that his university experience gave him perspectives which made his NS experience more meaningful. He also pointed out that despite his age, he did not face any problems interacting with younger servicemen.

There were suggestions to give all Singaporeans the choice of attending university, whether overseas or locally, before serving NS.

Either way, they will enter the job market at the same time.

But defence analyst Ho Shu Huang said this could give rise to "knock-on effects" - from unpredictable NS intake sizes to insufficient university places because of a sudden surge in demand.

And this may not be fair to everyone.

"Not all qualify for university. Allowing this group to defer would come across as being unfair," he said.

Some parents are also convinced of the benefits of serving NS first.

A 49-year-old mother, who wanted to be known only as Mrs Chia, said NS was good for her 19-year-old son.

She said that the stint allowed him to mature and gave him time to think about what he wanted to pursue in life.

Dominic Teo and Calvin Yang