In April, Alice Dreger—mom, bioethicist, activist, and professor at Chicago’s Northwestern University—sat in on her son’s abstinence sex ed class at East Lansing High School in Michigan. The misinformation being delivered by the visiting “educators” was so shocking, she began live tweeting it—and her outraged missives quickly went global and started a national debate on sex education in schools. Here’s her story.—Editor

Until recently, the only way I could find out what was going on in my son’s sex ed classes was by asking him about it. For example, in middle school, I learned he had to help the teacher explain something about sex anatomy when she was stumped. By the way, I’m a sex researcher studying intersex (those whose genitals do not fit the typical definitions of male or female), so he knows a lot about sex anatomy.

Now he’s a freshman in high school, and I’ve learned his sex ed is being taught in a health class by a gym teacher in conjunction with some “special helpers.” We were driving back from the vet with a pet rat suffering from a bad foot, when my son broke it to me: They’re teaching sexual abstinence in the class. It’s not abstinence only, but it may as well be.

I told my son why I think teaching teenagers abstinence is stupid, channeling my years of experience with the subject: (1) Sex is pleasurable, and there’s no good reason you should deny it to yourself if you have a consenting partner and you’re on the same page. (2) Marrying someone who you haven’t had sex with is a potential disaster. How do you know if you’re sexually compatible? (3) Whomever you love enough to marry deserves to have you well-practiced at sex before you marry.

My son nodded and remarked that, in class, he’d said to his classmate, “I can see I’m going to be spending some time with Google Scholar tonight.” Having heard previously about the ineffectiveness of abstinence education (again from me), he wanted to gather some data on the subject to present to the teachers. (What can I say? We’re a household of data geeks.)

So he and I sat down over dinner and did some looking together. We didn’t spend a ton of time on it, but we found a page that seemed to nicely sum up many of the potential problems with abstinence education and virginity pledges. I offered to come to class to see what they were teaching if he wanted me to—but only if he wanted me to.

He printed off copies of the webpage and said he was thinking of giving them to his teacher, guest teacher, and the principal.

In the morning, I asked whether he wanted me to come to class. He did. I told him I was just going to quietly observe, although I brought my computer so I could take notes. The regular class teacher was very nice, and I was seated in the back corner where I could watch without being in the way.

The visiting sex ed presenter—let’s call her Ms. Thomas—started class by asking if there were any questions from last time. My son’s hand shot up. He asked if her teaching of sexual practices was evidence-based.

Looking startled, she said yes.

“Then why are you teaching abstinence when it doesn’t decrease the amount of premarital sex and increases dangerous practices, including sex without contraception?” he said. He gave Ms. Thomas a copy of what he had brought.

“That’s not true,” she said. “You can look up anything on the internet.” She referred him instead to the National Abstinence Education Association’s website. (When I got home, I discovered it is a 501(c)(4) organization—a lobbying group that does things like trying to stop “anti-abstinence justices” from getting federal judgeships.)

The class began murmuring at my son’s attempt to challenge this visiting educator. To be honest, it didn’t strike me at first as particularly dramatic. He’s been raised to believe authority rests in good studies, not in individual humans, and he’s been challenging us since he was two years old. (“The earth does NOT move! The sun goes UP and DOWN!”) We’ve never said to him, “Don’t challenge me, boy!” We’ve always said, “What’s your evidence? I’ll show you mine.”

But Ms. Thomas didn’t want to discuss evidence. She wanted to move on, and move on she did. The kids were told they were going to continue to talk about “stories of abstinence” and “non-abstinence stories that led to consequences.”

And so we were presented with a visitor I’m going to call Jerry. Jerry told a genuinely sad story of how he was raised by an alcoholic father and got into alcohol and drugs at a young age. He hooked up with a girl “whose mother had put her on birth control.” But it failed, and she got pregnant. Jerry said he and his girl didn’t tell their parents as the pregnancy progressed.

Hold on a second: Her mother gave her birth control, but would be shocked she had sex? Clearly Jerry’s lesson here—the reason he needed to include that the girl had been on birth control but didn’t tell her mother when she got pregnant—was supposed to be this: Birth control fails. It fails all the time. And sex is so shameful that if you get pregnant, you can’t get prenatal care. You have to hide the pregnancy. In shame.

Jerry told us that once the girl “showed” and everyone found out, she was mocked and friends deserted her. If I followed this disaster story correctly, Jerry later went on to knock up another girl. Same basic story: another child they weren’t ready for, failure to finish school, failure to be employed, more drugs, more sex. One of his friends overdosed and was “a vegetable,” according to Jerry, for 11 years.

The upshot? Sex is just one disastrous component of “a bad lifestyle.”

But then—then!—Jerry met a beautiful girl he liked so much. And she had been raised in “the abstinence lifestyle.” He decided to put it back in his pants, woo her, and “put her on a pedestal.” After two long, chaste years, he married her. And then they had sex. And now have two kids.

The lesson Jerry wanted to impart? This: “You’ll find a good girl. If you find one who says 'no,’ that’s the one you want.”

He actually said that. If a girl says no, “that’s the one you want.”

Silly me! I’ve been teaching my son that if a girl says no, you exit politely and get the hell out of her space.

Now Ms. Thomas was up. She wanted to talk about birth control, which I thought was promising—it suggested a recognition that you can have sex without wanting a baby. But her message was also one of sexual doom: “It is absolutely better to use something rather than nothing if you have sex,” she said. “But condoms fail.”

Condoms fail 18 percent of the time, according to this woman. She noted that stats vary, but went with the big number anyway. She told the story of a couple of teens who came across a box of condoms in which every condom had a pinhole leak. They knew this because they filled them all with water first. (They must have been super turned on!) According to Ms. Thomas, the FDA allows condom manufacturers to have a failure rate of one box in 400. You, son—you might be the buyer of box 400.

(According to the CDC, condoms do have an 18 percent failure rate when used improperly—which is why a sex education class should cover how to use a condom correctly! Correct usage of condoms brings failure rate down to two percent, lower than most hormonal birth control methods.)

At this point, it became clear that while this was not technically abstinence-only sex education, it was terror-based sex education. By now, we had learned sex is associated with drug abuse, drug overdose, disease, unwanted pregnancy—pretty much every horror you can name except shingles and Lawrence Welk.

And that good girls say “no,” and you don’t want any slut who says “yes.”

Ms. Thomas’s dire warnings continued: “It takes only one sperm to fertilize an egg. It takes only one act of sex to get pregnant.”

I wanted to raise my hand and blurt out, “Not if it’s anal or oral!”

She moved on to a “game.” The game involved everyone getting a number from one to six. She rolled the dice. If your number came up, your condom failed. But your condom didn’t just fail—a pregnancy resulted. And from the pregnancy came a baby. When your number came up, you raised your hand and Ms. Thomas handed you a paper baby.

Within a few minutes, the entire class was preggers. Even the boys.

The bell rang. As kids cleared the room to get to their next class, I went up to calmly talk to these people. I failed. I started screaming and swearing. I feel bad about that. I’m glad my son takes after his father and doesn’t mimic me in such situations.

But what I’d just seen was worse than anything I’d expected in a progressive school district in a liberal college town. I mean, here’s what these visiting “educators” were telling those kids: Condoms fail. They fail so often, they are pointless. There is no birth control except condoms. So if you have sex, you will end up with a pregnancy, and there is no abortion—you have to have that baby. And you will be shamed.

And what about that bit about wanting a “good girl” who says “no”? What year is this?

I remember when a friend of mine (whose gay daughter also goes to my son’s school) tried to nudge me to pay attention to sex ed—but I told her I was too busy. Another friend told me about a “Gender Equity” club forming at the high school; a group of students trying to agitate for positive change in sexuality and gender issues. I’d reacted again with “I’m too busy.” Honestly, I’m sure that after my son’s “no-means-yes” sex ed class ended, I was yelling and swearing at the visiting teachers partly out of sheer guilt.

Once home, I worried about how my kid was doing after challenging Ms. Thomas and being rebuffed. But I shouldn’t have been worried; he came home five hours later with a smile.

“The news got to the locker commons before I got there,” he said.

What news? The news that he’d challenged the teachers with information. I’d missed that, in addition to what he’d said in class, he’d also passed out information to all his classmates so they could read what he’d found out about abstinence education and virginity pledges—and how they don’t really help.

At this point, I confessed that I’d tweeted about the whole thing and it had gone national while he was at school. He cracked up. He especially enjoyed hearing about the Twitter math geeks who were calculating the odds of a classroom of 20 kids all experiencing condom failure and getting pregnant in a few dice rolls. It came to about one in three billion.

We went for ice cream and, on the way home, swung by the drugstore. I bought him a box of condoms.

“You know what my friends and I are going to do with those. We’re going to make water balloons and cover stuff as a joke,” he said.

“Then we’ll get the non-lubricated kind,” I answered.

Back at home, he continued his internet research and found a meta-analysis of 13 studies on abstinence education in the medical journal BMJ. He went over it with his father, who is a physician. I gave him the information on the website Ms. Thomas had referred him to—showing him that it’s a political lobbying group. And I noticed for the first time my son was wearing a shirt my brother gave him: “Stand back—I’m going to try science.”

His father warned him: “Tomorrow, you can’t expect the adults in the room to act rational. They have their emotions tied up with this, and whatever evidence you bring isn’t going to convince them. Just be prepared for that.”

Our son said he was prepared, and that convincing them wasn’t his goal. His goal was to teach the other kids some of the truth, and also to let them know it’s okay to challenge authority.

Me? I’m kicking myself now for not having gone to all those school-board meetings where they talked about the sex ed curriculum. But I wonder if it would have mattered—because whatever they write in the curriculum plan, what matters is where the rubber meets Ms. Thomas.

When the school board approved this curriculum that included condom use, I’m sure Jerry’s story was not run by them—especially not the slut-shaming bit about “good girls.” And just to be clear, there were visitors earlier in the week who were good. My son tells me they had someone talk personally about abusive relationships, and it was very useful and powerful.

For liberal parents like me, the mistake we make is thinking of ourselves as the kind of people who don’t interfere in public schools. As a consequence, the only people who do interfere with sex ed curricula are 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.

We’re going to need more than my kid and his printouts to teach this generation.

Alice Dreger is author of the new book Galileo’s Middle Finger: Heretics, Activists, and the Search for Justice in Science (named one of the “best books of the month” in nonfiction by Amazon). Follow her on Twitter @AliceDreger.