As if on cue, all faces turn alertly toward the front of the classroom where Bridget Brownell has set up a slide show at Taft High School in Woodland Hills.
They are about to view diseased sex organs.
"First," she said, "let me take attendance, and then I will shock you."
Brownell belongs to a declining breed: She's a certified health instructor leading a one-semester health class in a California public high school. The Los Angeles Unified School District nearly killed health as a required course, to focus more on its new mandate that all students complete college-prep classes. Other school systems have stopped requiring health class simply to save money.
With or without a health course, California high schools are required by law to teach students about AIDS and other sexually transmitted diseases; they face penalties if they don't.
Schools also are supposed to teach such topics as nutrition, safety, mental health awareness and about drug, alcohol and tobacco abuse. But generally there's no penalty for skipping these topics, and experts believe many have long done so. They also said more schools and districts are dropping health class, although there's no official tabulation.
In interviews at several high schools, some students said they didn't learn much new in health. A majority, however, said they found it valuable, even if they were initially skeptical. Several also admitted they probably would not have taken it if they didn't have to.
Long Beach Unified last year made health an elective rather than a requirement, to save money. Numerous other school systems also don't require the class. Nor do many independent charter schools.
"When Long Beach lost their health requirement, it was a big blow," said Mary Marks, a health education consultant at the California Department of Education. "Health has been one of the early and continuing hits as money has gotten tighter and tighter."
In L.A. Unified, the class has been eliminated at most high schools managed by a nonprofit under the control of L.A. Mayor Antonio Villaraigosa, falling victim to finding more time to help struggling ninth-graders — the grade level at which health is typically taught.
"Less than 10% of our kids are at grade level in math," said Marshall Tuck, head of the mayor's Partnership for Los Angeles Schools. "If you don't get them caught up early, they're going to fall further behind. All of us are forced to make really difficult decisions."
Instead of a dedicated class, these schools, like those in Long Beach and other districts, incorporate health topics into other classes, which can extend health education beyond ninth grade, said officials who've dropped the requirement.
The mayor's schools also have appealed for help from outside organizations, such as Planned Parenthood, which provides counseling and referrals at Roosevelt High.
About 400 certified instructors are teaching health in L.A. Unified, with the number trending downward, said Timothy Kordic, who heads the district's HIV/AIDS Prevention Unit.
"Health is probably one of the only classes in the entire curriculum that is about kids," said longtime Birmingham High health teacher Wayne Sink, who's retired but still volunteers at the school. "It is all about their lives and what is going on about diet, nutrition, puberty, sexuality, dating — all those things they were going through. It's vital."
In sophomore Kelly Medina's health class last year, "they gave us a 'baby' to take care of," she said. If students hit the "baby," "we would get an 'F' or a 'D.' I learned not to have babies when we're teens."
At her school, Jordan High in Watts, there's no health class this year. The campus is split between a school run by the mayor's nonprofit and a separate academy managed by Green Dot Public Schools, an independent charter operator. Green Dot incorporates the required health units in other classes, so there are more resources and time for college prep courses.
Topics in Brownell's class, meanwhile, run the gamut: nutrition, anatomy and physiology, bullying, healthy decision-making, birth control, mental health, anger and stress management, and tolerance — L.A. Unified pioneered teaching students to accept gay, bisexual and transgender peers.
L.A. schools Supt. John Deasy canceled plans to drop the health requirement after resistance from the Board of Education and after teachers, parents and students descended on board meetings.
"It's the course in which we're able to deal with a host of important issues that I don't have other ways to deal with," Deasy said.
Brownell's arsenal includes a text, workbook, and materials and props she's assembled, such as eyeglasses that simulate the reduced perceptions of a drunk driver.
Her students recently painted a "safe sex" mural on campus, and they engage in role-playing, "like one of us wanted to have sex and the other didn't," said junior Alex Sandoval, 16.
Students said they appreciate Brownell's expertise, availability and, as needed, confidentiality.
In her class, Taft sophomore Jessica Bandarizadeh said that "the first thing that came up was 'vagina' and 'penis,' and we were laughing so hard — it was so embarrassing." But by the end, the 16-year-old said, "We were so comfortable speaking about everything. It was almost like we grew up."
Her immigrant parents are not comfortable with such conversations.
"There's no sex before marriage in their eyes," Jessica said. "Even if you have trust with your parents, there are some things you can't talk about. I think my parents are happy I'm taking health."