Apparently, this is what could go wrong.
Crane High School in Crane, Texas is experiencing an outbreak of a sexually transmitted disease for a reason that you can probably envision.
Students at the school are only offered (not mandated) three days of sexual education each year and each of those three days are focused on abstinence only.
In an interview with My San Antonio on Monday, the superintendent of Crane Independent School District, Jim T. Rumage, said that abstinence education is still the best approach for students, regardless of the current outbreak. “If kids are not having any sexual activity, they can’t get this disease,” Rumage said. “That’s not a bad program.”
They clearly are having "sexual activity" and will continue to do so because that's what teenagers think about every single day.
I was going to say the superintendent is a man out of time, but I'm skeptical that there was ever a time when teenagers were the good puritans he imagines they should be.
Chances are good that the parents and school officials who prescribe abstinence-only education were not.