Last week, two 5th-grade girls addressed the Atlanta school board, asking that the board change the dress code so that girls might be allowed to wear skintight leggings, which are currently prohibited unless girls are wearing a skirt or shorts over the leggings. The board will announce its decision in January.

Three weeks ago, I led a full-day statewide conference in Illinois, hosted by the Illinois State Board of , and attended by more than 100 school administrators from across the state. I learned that the public schools in Evanston, Illinois have adopted a new dress code that allows students to wear almost anything they want, as long as the genitalia and the nipple of the breast are covered in opaque fabric. As a result, I was told, it is now common for girls to come to school wearing skintight leggings and a tight camisole that begins just above the breasts and ends above the belly button. That confirms my observations at more than 400 schools over the past 16 years. In 2001, it would have been unusual for a teenage girl to come to school wearing a very short skirt and a sheer mesh top, with the bra visible beneath the mesh. Now it’s becoming common.

Barbara Fredrickson and her colleagues at the University of Michigan conducted a study that bears on this issue. They randomly assigned college women and men to wear either a bulky sweater or a swimsuit. The men wore swim trunks, the women wore one-piece bathing suits. Each volunteer was seated in a small room: no windows, no observers. Each volunteer was then asked to take a math quiz. Fredrickson and her team then compared how women wearing swimsuits performed on the quiz compared with women who were wearing bulky sweaters, and likewise for the men.

What happened? The men who were wearing swim trunks did slightly better than the men who were wearing bulky sweaters. The women who were wearing swimsuits did much worse than the women who were wearing bulky sweaters: they got only about half as many questions right as the women who were wearing sweaters. And remember, the women in this study were in a closed room with no windows and no observers. Subsequent research has replicated and extended this finding.

We actually have quite a bit of research now on what happens when a girl or woman wears skintight leggings or a swimsuit. Often what happens is “self-objectification”: the girl, or woman, assesses herself as an object on display for others. And the more public the setting, the more likely self-objectification is to occur.

Self-objectification is distracting. It’s hard to concentrate on Spanish grammar when you’re wondering whether this outfit makes your thighs look fat. Girls who self-objectify are more likely to become depressed. They are less likely to be satisfied with their body. They are more likely to engage in self-harm.

Parents: please explain to your daughters, and to your sons, that it's not a good idea to go to school wearing revealing clothes, regardless of the policy of the school district. Don’t hesitate to play the role of the strict parent, if necessary. When your daughter goes to school wearing loose-fitting slacks and a baggy sweater, while her girlfriend is wearing leggings and a tight camisole and nothing else, and the other girl asks your daughter “Why are you wearing that?”—it’s not reasonable to expect your daughter to answer primly, “Researchers have found that girls who wear revealing clothes are more likely to self-objectify and to suffer various other adverse outcomes.” It’s much easier for her to say, “I didn’t want to wear this stupid outfit! My evil parents made me do it!”

When I visit schools and speak with students, some girls have told me that they resent the restrictions of the dress code. They feel that the prohibitions on wearing leggings, hot pants, brassiere tops, etc. (where such prohibitions still exist) are in place to prevent the boys from being distracted. I share the relevant research with those girls. I tell them: The most important issue here is not whether girls who wear leggings and brassiere tops are distracting the boys. The more important question is whether girls are distracting themselves. And the evidence suggests that they may be.