And it has also highlighted disparity in the law of rape, which makes it impossible for a woman to be accused of the crime.
Present legislation stipulates the crime of rape applies only when men force sex. In contrast, women who force an unwilling partner to have sex face charges of sexual violation. Both carry a maximum sentence of 20 years but only men can be charged with rape.
The Weekend Herald has chosen not to name the South Auckland school to protect the privacy of the children - the baby and the father.
Child Youth and Family confirmed it was dealing with a case at the school and that it was before the courts. It refused to make further comment, as did police.
The principal said he was shocked when the child revealed the details.
The boy approached him in his office about two-thirds of the way through the 2012 school year and told the principal he had a disclosure to make.
"You won't be very happy with me," he recalled the boy saying. He said he had been having sex with his friend's mother "and it needs to stop".
The principal said the boy was "very aware" of the situation he was in and determined he wanted the contact to end.
The Weekend Herald was told that the contact between the boy and the woman began about April last year, when the boy was aged 11. The woman's son took a day off school and encouraged his friend to do likewise, spending the day at his home.
During the course of the day, the woman gave the boy beer to drink and then later took part in a sexual encounter with him.
The sexual contact continued for a number of months after the initial encounter, the Weekend Herald was told. The boy had turned 12 by the time the child was born. CYF took a baby into care about two months ago.
The principal confirmed the details. "We got CYF involved the minute we found out about it."
Emails exchanged with a Child Youth and Family social worker, since retired, confirm the agency was involved. The CYF worker said police would be investigating - but also said the woman denied the sexual contact.
Male Survivors of Sexual Abuse manager Ken Clearwater said if the case were proved, the woman should be held accountable for her actions. Making charges able to be brought dependent on the gender of the offender was wrong and the law should be changed. "It is a huge issue for us."
He said male victims of sex abuse carried out by women were equally as damaged as any other victim of rape.
"As a male you're supposed to enjoy it but we don't say that about young girls. Males are not seen as victims. The psychological damage is huge - and they carry extra shale because it's a woman and you're supposed to enjoy it."
Mr Clearwater said most abuse of the sort in this case was not reported. He said the way the boy disclosed to the principal underscored the way in which the abuse was perceived. By saying "you won't be very happy with me", Mr Clearwater said the boy appeared to believe he was the one who had acted wrongly.
Mr Clearwater said the psychological impact would expose the boy to added risk of alcohol and drug abuse, relationship problems, anger and other mental health issues.
The executive director of Rape Prevention Education, Dr Kim McGregor, said male survivors of sexual offending by women often felt the abuse they suffered was minimised by society. "Just because sexual violence has been perpetrated by a female doesn't make it any less violent."
Manukau-based family lawyer Jeremy Sutton said under the law the boy would not have rights to the child unless he was present at the birth. He said he would have to make a case for access. He also said there were exemptions from child support for victims of sexual offending.
Liggins Institute director Professor Wayne Cutfield, an expert in the development of children, said boys became fertile about halfway through puberty, which could begin as early as age nine. "The onset of puberty is a lot younger than people think."
Statistics New Zealand does not hold data on the ages of fatherhood, only of motherhood.
