Frustrated by such stories, I asked a high school senior how she would feel if guys expected girls to, say, fetch a glass of water from the kitchen whenever they were together yet never (or only grudgingly) offered to do so in return? She burst out laughing. “Well, I guess when you put it that way,” she said.

The rise of oral sex, as well as its demotion to an act less intimate than intercourse, was among the most significant transformations in American sexual behavior during the 20th century. In the 21st, the biggest change appears to be an increase in anal sex. In 1992, 16 percent of women aged 18 to 24 said they had tried anal sex. Today, according to the Indiana University study, 20 percent of women 18 to 19 have, and by ages 20 to 24 it’s up to 40 percent.

A 2014 study of 16- to 18-year-old heterosexuals — and can we just pause a moment to consider just how young that is? — published in a British medical journal found that it was mainly boys who pushed for “fifth base,” approaching it less as a form of intimacy with a partner (who they assumed would both need to be and could be coerced into it) than a competition with other boys. They expected girls to endure the act, which young women in the study consistently reported as painful. Both sexes blamed the girls themselves for the discomfort, calling them “naïve or flawed,” unable to “relax.”

According to Debby Herbenick, director of the Center for Sexual Health Promotion at Indiana University and one of the researchers on its sexual behavior survey, when anal sex is included, 70 percent of women report pain in their sexual encounters. Even when it’s not, about a third of young women experience pain, as opposed to about 5 percent of men. What’s more, according to Sara McClelland, a psychologist at the University of Michigan, college women are more likely than men to use their partner’s physical pleasure as the yardstick for their satisfaction, saying things like “If he’s sexually satisfied, then I’m sexually satisfied.” Men are more likely to measure satisfaction by their own orgasm.

Professor McClelland writes about sexuality as a matter of “intimate justice.” It touches on fundamental issues of gender inequality, economic disparity, violence, bodily integrity, physical and mental health, self-efficacy and power dynamics in our most personal relationships, whether they last two hours or 20 years. She asks us to consider: Who has the right to engage in sexual behavior? Who has the right to enjoy it? Who is the primary beneficiary of the experience? Who feels deserving? How does each partner define “good enough”? Those are thorny questions when looking at female sexuality at any age, but particularly when considering girls’ formative experiences.

We are learning to support girls as they “lean in” educationally and professionally, yet in this most personal of realms, we allow them to topple. It is almost as if parents believe that if they don’t tell their daughters that sex should feel good, they won’t find out. And perhaps that’s correct: They don’t, not easily anyway. But the outcome is hardly what adults could have hoped.

What if we went the other way? What if we spoke to kids about sex more instead of less, what if we could normalize it, integrate it into everyday life and shift our thinking in the ways that we (mostly) have about women’s public roles? Because the truth is, the more frankly and fully teachers, parents and doctors talk to young people about sexuality, the more likely kids are both to delay sexual activity and to behave responsibly and ethically when they do engage in it.