SHE was meant to sit there and observe, but when Alice Dreger heard the “advice” being delivered during her son’s sex education class this week, she let rip.

Armed with her computer, Dreger, a medical humanities and bioethics professor at Northwestern University in the US, couldn’t contain her disbelief at what was being dished out as fact, so she took to Twitter.

In her early tweets, Dreger starts out calmly, citing how the teacher is telling the students that abstinence is the best defence against unwanted pregnancy.

Then, as the class progresses, her posts become more colourful.

WARNING: Bad language in some tweets below

The visitor-teacher is telling my kid abstinence education reduces premarital sex. My kid is trying to show her studies that dispute that. — Alice Dreger (@AliceDreger) April 15, 2015

She's being completely condescending. "You can look up anything on the internet" Then refers him to site on abstinence education! — Alice Dreger (@AliceDreger) April 15, 2015

The whole lesson here is "sex is part of a terrible lifestyle. Drugs, unemployment, failure to finish school -- sex is part of the disaster" — Alice Dreger (@AliceDreger) April 15, 2015

Then came the comment that sent Dreger ballistic - that good girls say no.

"You'll find a good girl. If you find one that says 'no,' that's the one you want." HE ACTUALLY JUST SAID THAT. — Alice Dreger (@AliceDreger) April 15, 2015

When the female health teacher began her speech, things only got worse.

Now the woman is up. "Sometimes condoms fail." — Alice Dreger (@AliceDreger) April 15, 2015

She's now telling story of condom box in which EVERY SINGLE CONDOM HAD A HOLE. — Alice Dreger (@AliceDreger) April 15, 2015

"On average 1 out of 6 times there is a mishap with a condom." "Every day in US 1600+ teen pregnancies." Lesson: condoms fail? WTF? — Alice Dreger (@AliceDreger) April 15, 2015

"We are going to roll this dice 8 times. Every time your number comes up, in pretend your condom failed and you get a paper baby." JESUS!!! — Alice Dreger (@AliceDreger) April 15, 2015

Paper babies are being handed out to EVERYONE. They have ALL HAD CONDOM FAILURE AND THE WHOLE CLASS IS PREGNANT. — Alice Dreger (@AliceDreger) April 15, 2015

Dreger’s rolling coverage subsequently went viral and caused a stir in her town in east Lansing.

In one of her tweets, Dreger says the local paper wrote a story “shaming” her for live tweeting the pro-abstinence sex education lesson.

She has also now been banned from her son’s school after she swore during her outburst after the class ended.

In the meantime I've been banned from the high school (except for drop off/pick up/concerts/conferences) for saying 'fuck' after class. — Alice Dreger (@AliceDreger) April 16, 2015

But Dreger has taken it in her stride posting on Twitter that her partner thinks the school has plastered a picture of her at reception with a caption saying “Don’t let this woman in”.

Dreger also wrote about the experience for TheStranger.com where she encourages other parents to question what is being taught in today’s schools, especially regarding sex education.

“Liberal parents like me, the mistake we make is thinking of ourselves as the kind of people who don’t interfere in public schools,” she wrote. “As a consequence, the only people who do interfere with sex-ed curriculums are the conservatives.

“If people like me — people who want to see sex ed include teaching about masturbation, the pleasure urge, the existence of LGBT people — don’t show up and push our side, the ‘middle ground’ turns out to be damned near the right.”