Another liberal narrative got deflated last week when the National Bureau of Economic Research showed that the distribution of free condoms at high schools seemed to be correlated with a significant increase in teen pregnancy and a rise in sexually transmitted diseases.

Liberals immediately rushed to explain away the findings. After all, the idea that the widespread availability of contraception for kids would have a perverse effect would be a blow to what intellectual elites have insisted for more than four decades.

At Vox.com, Sarah Kliff explained that some “social conservatives” might believe that “free condoms encouraged teenagers to engage in riskier behavior than they would have otherwise — with the condoms available, they could possibly decide to have sex in situations where they otherwise wouldn’t.”

But then she dismissed such silliness immediately, citing the results of one 1998 study of the sexual behavior of students at a high school in Los Angeles. The NBER study, though, was based on a national data set that included thousands of schools. Hard to ignore or explain away.

But that didn’t stop Slate’s Christina Cauterucci from trying. She suggested free condoms helped teenagers who were “too shy to buy condoms but reluctant to have sex without them,” or teens who wanted to avoid talking to their parents about sex and so couldn’t go see a doctor to get a more effective form of contraception.

But there’s no acknowledgment of the possibility that teens might get pregnant more because they might be having sex more and they might be having sex more because they’re surrounded by adults who say casual sex is no big deal.

More generally, though, there’s no reason to think that the greater availability of contraception in high school has a different effect than the greater availability of contraception for the general public.

A 1996 paper co-authored by Nobel Laureate George Akerlof and current Fed chair Janet Yellen suggests that contraception makes sex cheaper and leads to more sex — and thus to more non-marital childbearing. The two attributed the rise in out-of-wedlock births in the 1970s to laws that permitted unmarried couples access to contraception and liberalized abortion laws.

They wrote: “Although many observers expected liberalized abortion and contraception to lead to fewer out-of-wedlock births, the opposite happened — because of the erosion in the custom of shotgun marriages.” As a result of the widespread availability of abortion and contraception, “sexual activity without commitment was increasingly expected in premarital relationships.”

The widespread availability of contraception in high schools has had largely the same effect.

The NBER paper’s authors note that much of this increase in fertility comes from schools that passed out condoms for free without mandating that they be accompanied by counseling.

“Counseling” here could mean anything from instructions about how to put on a condom to a longer course on the importance of safe sex.

In other words, liberals will now argue that the problem is not with the distribution of condoms. It’s that we didn’t offer enough sex education with them.

But this, too, hasn’t been borne out. As Jonathan Zimmerman noted in his 2015 work, “Too Hot to Handle: A Global History of Sex Education,” there’s “scant evidence” that sex education “affects teen pregnancy or venereal disease rates.”

The NBER authors are correct that condoms are among the least effective forms of birth control, in part because they’re often used incorrectly. And because they’re handled by boys who have much less incentive to get the whole birth-control thing right.

But this still isn’t a reason to offer more counseling at public schools.

Leave aside the idea that many parents would rather not have their kids listen to their teachers demonstrate proper condom technique — or force their kids out of the room when the demonstrations are going on.

The truth is that oral contraceptives are more effective and LARCs (long-acting reversible contraceptives) are even more effective than those. These methods are handled by doctors, not 9th-grade teachers. The prescription of these contraceptives involves — one hopes — serious conversations with teenagers by responsible adults trying to help them make the right choices for their lives, not just lecturing a giggling class.

When I was in high school, I recall a performance of a sex-ed play in which the actors placed condoms on bananas and at one memorable moment one tossed a bucket of prophylactics into the air and announced, “There are so many kinds to choose from.”

If only we understood the exciting variety and easy availability of condoms out there, then we’d be sure to have safe sex. One more liberal piety down the drain.

Naomi Schaefer Riley is a senior fellow at the Independent Women’s Forum.