Senate Republicans have a new plan for preventing mass shootings: require public schools to use surveillance technology to monitor students’ online behavior for signs of violence or self-harm.

A new Republican bill that claims “to help prevent mass shootings” includes no new gun control measures. Instead, Republican lawmakers are supporting a huge, federally mandated boost to America’s growing school surveillance industry.

Millions of American students, across thousands of school districts, are already being monitored by tech companies that scan everything they write in school emails, chats and shared documents, looking for signs of suicidal thoughts or plans for a school shooting. This surveillance technology doesn’t turn off when the school day is over: anything students type in official school accounts is monitored 24 hours a day, whether they are in their classrooms or their bedrooms.

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There is still no research evidence that demonstrates whether or not online monitoring of schoolchildren actually works to prevent violence.

Despite this, new legislation introduced Wednesday by Senator John Cornyn, a Texas Republican and longtime ally of the National Rifle Association (NRA), would update the Children’s Internet Protection Act to mandate that public schools adopt “a technology protection measure that detects online activities of minors who are at risk of committing self-harm or extreme violence against others”.

A spokesperson for Cornyn did not immediately respond to a request for comment on why he and other Senate Republicans are mandating that public schools adopt a new technology before there is any clear evidence that it’s effective in preventing violence.

The Cornyn bill, entitled the Response Act, includes a range of other policies without strong evidence of reducing mass shootings, including expediting the federal death penalty for perpetrators of mass shootings, a priority of Donald Trump.

Privacy advocates say pervasive surveillance is not appropriate for an educational setting, and that it may actually harm children, particularly students with disabilities and students of color, who are already disproportionately targeted with school disciplinary measures.

“You are forcing schools into a position where they would have to surveil by default,” said Amelia Vance, the director of education privacy at the Future of Privacy Forum.

“There’s a privacy debate to be had about whether surveillance is the right tactic to take in schools, whether it inhibits students trust in their schools and their ability to learn,” Vance said. But “the bottom line,” she said, is “we do not have evidence that violence prediction works”.

There’s no hard data on how many public schools are already monitoring what students write 24 hours a day. But Vance estimates that only a third of US school districts, at most, currently use this technology.

If Cornyn’s bill becomes law, “you’re going to force probably 10,000 districts to buy a new product that they’re going to have to implement”, she said.

That would mean redirecting public schools’ time and money away from strategies that are backed by evidence, such as supporting mental health and counseling services, and towards dealing with surveillance technologies, which often produce many false alarms, like alerts about essays on To Kill a Mockingbird.

Fear of school shootings has already fueled rapid growth in the school surveillance industry, particularly after a school shooting in Parkland, Florida, last year left 17 people dead. Companies that sell this technology are marketing it to schools with bold claims of lives saved – numbers based only on internal, anecdotal estimates, not independent analysis.

One leading school surveillance company, Gaggle, says its technology is currently used to monitor 4.5 million students across 1,400 school districts. The company claims that in the last academic year alone its technology “helped districts save the lives of more than 700 students who were planning or actually attempting suicide”.

Securly, another company, says its products are used to protect 10 million students across 10,000 individual schools. In the past year, Securly said it helped school officials intervene in 400 situations that presented an “imminent threat”.

Another company, Bark says it works with at least 1,400 school districts across the country, and claims its technology has helped prevent “16 credible school shootings” and detected “twenty thousand severe self-harm situations”. Bark, which sells a for-profit app to help parents monitor what their children are doing online, offers its surveillance technology to schools for free.

First passed in 2000, the Children’s Internet Protection Act was originally designed to make sure that American kids would not be looking at porn on taxpayer-funded school computers. It currently requires schools to monitor students’ “online activities”, although privacy experts say that what that means – and what constitutional limits there may be on the monitoring – have never been clearly defined.