Fewer than one-fifth of middle schools — and half of high schools — are teaching all of the sex education topics recommended by the Centers for Disease Control and Prevention, a new study reveals.

The CDC report found that, for every age group, the least likely topics to be taught were how to get and use condoms.

The results, from the 2013-14 school year, did not surprise Stephanie Zaza, the director of the CDC's Division of Adolescent and School Health, who oversaw the survey administration. "As far back as I can recall," she says of the low rates of compliance, "it's been pretty flat."

The research confirms what students like Marcella Morales-Lugo in New York City have long experienced. Her first sex-education class was in eighth grade, and, as so often happens, it was taught by her physical education teacher.

"It was a little awkward," recalls Morales-Lugo, now a high school senior. "One period she was telling me to do jumping jacks and the next she was telling me about gonorrhea."

The class, she adds, was too little, too late: "I started to see my girlfriends getting pregnant, and this is middle school. It broke my heart."

As part of its biennial school health profile, the CDC asked all states to survey school health educators on what they teach to students when it comes to sex. Ultimately, 44 states had enough respondents to be included in the data, which also looked at certain large urban school districts and U.S. territories.

The survey listed 16 recommended topics as critical to sexual health, falling under four broad subject areas: HIV prevention, STD prevention, pregnancy prevention and information on sexuality.

The findings offer a glimpse inside thousands of classrooms to reveal that what gets taught about sex — often decided at the district level — varies widely nationwide.

For example, the study found that Kentucky had the lowest rate of the states surveyed for teaching middle schoolers the full range of recommended material, at just under 4 percent. North Carolina had the highest rate for middle schoolers, with over 45 percent.

In high school, the gap is even wider. In New Jersey, 9 out of 10 high school students receive the full list of recommended topics. Arizona was lowest in the survey, with fewer than 1 in 5 students.

Zaza says there's a variety of reasons why sex education is sometimes put on the back burner, including a lack of time or qualified staff, or restrictive policies.

But, she argues, it's critical for schools to have these conversations with students early.

Young people are a high-risk population when it comes to sexual health: Nearly half of high school students say they have had sex, and half of all new sexually transmitted infections occur in people ages 24 and younger.

"We can actually help prepare students and help them avoid these risks," she says, "if we can do a good job educating them before they become sexually active."

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