Gov. Ron DeSantis signed a bill Wednesday that'll let more Florida teachers carry guns in school, the latest response to last year's mass shooting at Marjory Stoneman Douglas High School in Parkland.

DeSantis signed the bill in private and issued no statement. The Republican-led Florida House of Representatives voted to send the bill to the governor last week, while the GOP-controlled state Senate passed the measure the week before.

The new law expands an existing school "guardian" program and allows any teacher to volunteer to carry a weapon if his or her school district approves. Would-be volunteers must undergo at least 144 hours of police-style training, psychiatric evaluation and drug screening. Under a previous law, passed immediately after the February 2018 Parkland shooting, only teachers who had another role at school, such as sports coach, were eligible to carry weapons on campus.

The new law expands the program to make all teachers eligible regardless of whether they have a non-classroom role.

The bill was opposed by most Democrats and teachers' unions, which argued that the introduction of more weapons in schools would place children at risk, increase the dangers of mistaken shootings and lead to more violence against African-American students because of inherent biases. Supporters of the bill said arming teachers is the best way to protect children from future school shooters. Republicans emphasized that the program is voluntary, and that law enforcement in some rural districts could be 15 minutes or more from a school if a shooter attacks.

It's unclear how many Florida school districts in the state will approve of expanding the "guardian" program. Currently, 25 of the state's 67 school districts take part in the program, but boards in some of Florida's most populous counties have already opted out, preferring to use trained police officers for school security.

"Can you imagine somebody you taught potentially coming on the campus and you ... protecting other children and shooting a child you once taught?" Stephanie Baxter-Jenkins of the Hillsborough County Classroom Teachers Association told Fox News this week. "We're not thinking about all the mental issues that go into that."

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"We also have kids that come from places where school is the only safe space that they have," Baxter-Jenkins said, "so turning that into a different scenario -- we don't think is healthy for kids mentally."

The new law also contains a number of other school safety measures, such as wider disclosure of certain student mental health records and mental screening of troubled students. It also mandates greater reporting of school safety and student discipline incidents and a requirement that law enforcement officials be consulted about any threats.

Fox News' Allie Raffa and The Associated Press contributed to this report.