How could any responsible person oppose a measure that might prevent a school shooting? When framed that way, the decision of the Philadelphia Board of Education to require all district high schools to use metal detectors doesn’t seem controversial. The fact that the students whom the metal detectors are intended to protect protested the decision illustrates the conundrum that our age of unspeakable violence has created.

Last week, the Philadelphia Board of Education voted to require that all schools use metal detectors. While all 49 high schools in the Philadelphia school district have metal detectors, three don’t actively use them. The Science Leadership Academy, one of the city’s most reputable magnet schools, is one of these three. SLA is moving from Center City to an unused part of the Ben Franklin school on North Broad. The board wanted to set a standard to prevent a situation in which after the SLA move, students in the same facility would be treated differently — with some required to go through a metal detector and some not.

Student activists, on the other hand, argue that metal detectors erode the trust between schools and students. Because the students themselves are usually the ones being screened, they say that installing metal detectors signal that they are viewed as threats. The two nonvoting student members of the board opposed the decision.

There isn’t a lot of research about the positive or negative safety or social effects of metal detectors in schools. A review of the evidence published in the journal of the American School Health Association found mixed results. While one study did find that fewer students carry weapons to schools that do use metal detectors than schools that do not, that reduction did not translate to less violence in schools.

The sad fact is that metal detectors won’t prevent the most frequent form of violence in schools, such as bullying. Some experts believe that they also are unlikely to prevent the most severe, such as a mass shootings. If someone with a semiautomatic weapon is motivated to shoot up a school, the students in line for the metal detector and the operator would likely be the first victims. It’s impossible to know what the outcome would have been if places like Newtown, Conn., or Parkland, Fla., had metal detectors, but detectors might have slowed down the path of destruction.

Everytown for Gun Safety has tracked at least 431 incidents of gunfire on school grounds in the past six years.

Metal detectors, like body scanners in airports and other more intrusive forms of security monitoring, are ugly reminders that something is terribly wrong — making them terribly necessary.

But as long as there are metal detectors in school, all students should be treated equally — magnet or not. The ultimate goal, though, must be to make metal detectors in schools obsolete. That would require interventions, such as addressing the behavioral needs of students. It would also require Harrisburg to enact gun-control measures. Until then, we will continue spending education dollars on security measures, not books.