One student griped that the workbook they were given seemed to promote the organisation's beliefs rather than present facts.

The student, who declined to be named and goes simply by his online moniker Cygig, started the active thread on the online forum at www.spug.net

He said in one posting: 'It seemed like I was being brainwashed.'

His schoolmate, Tay Wei Kiat, said: 'They did not clearly state the source of their opinions and instead attempted to spread their beliefs to everyone attending the workshop by asking everyone, regardless of their individual beliefs or religion, to write down things like 'I must condemn masturbation and in-vitro fertilisation'.'

They admitted that large parts of the programme - which focused on goal-setting and abstinence - were fine. Their beef was with isolated statements.

For example, the programme workbook had this to say about contraception: 'The sterilised sexual act is not much different in its meaning from an act of mutual masturbation whereby the couple seeks to use each other (their bodies) to derive sexual pleasure.'

Another section listed 'adult instead of embryonic stem-cell research' alongside 'absolute respect for life' and 'life is a gift' as things to 'promote, protect and cherish'.

According to Mrs Woo Soo Min, vice-principal of Anderson Junior College, the school had also received feedback that mirrored the views expressed online.

She explained that the Family Life Society was chosen because 'it focused on abstinence and approached the topic using one's values and beliefs as the basis', but conceded that the tone might not have been suitable.

However, she stressed: 'The content raised merely represents a certain viewpoint and we see our role as educating and exposing students to a range of viewpoints.' She would not say if the school would get the group to conduct further talks.

Under Ministry of Education guidelines, schools are expected to provide eight hours of sexuality education to upper secondary students and four hours to tertiary students. However, many schools are going above and beyond the time requirements - often engaging external vendors to do so.

When contacted by The Sunday Times, Family Life Society defended its programme, saying that it never imposed any ideas on the students and had kept its content entirely secular.

'I don't see how it would work otherwise,' said Mr Andrew Kong, a senior executive in the society. 'Even I would be put off if someone tried to tell me these things while quoting from a religion.' He added that while some parts may have been 'moralistic', they were never 'religious'.

He also said that every talk kicks off with a disclaimer.

'We tell them every time that whatever views they don't agree with, they don't have to accept. In one ear and out the other.'

Indeed, not everyone who attended the talk took issue with it.

Jane Wu, 18, said: 'I did not agree with everything that was said, but I don't necessarily mind sitting there listening to it.'

Four other schools which had engaged Family Life Society to speak to their students - Hai Seng Catholic School, Orchid Park Secondary, Westwood Secondary and Bukit Batok Secondary - received no complaints.

Other groups conducting similar classes - Focus on the Family, A Life and Synergy Coaching - said they do not go so far as to bring up morality.

Mr Jay Abdul Rahman, 35, chief coach at Synergy Coaching, said: 'From the start I make it clear that I am approaching it from just a secular point of view. I may be Muslim but if a student asks me about masturbation, I will tell him it's natural.'

He added: 'I think the best way is not to try to shove the message down their throats. We should just equip them with enough information for them to make the choice for themselves.'