The tremors of the Uvalde school shooting have been felt in schools across the United States, with many boosting security measures. A range of new strategies have been introduced to protect young students from mass shooters.

The Uvalde shooting resulted in the death of more than 20 people, most of whom were children in the fourth grade. Two teachers were also killed by Salvador Ramos, who was identified as the 18-year-old gunman.

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El Paso, a city in Texas that connects the US to Mexico, has taken drastic measures to ramp up security. In addition to increased patrolling, officers have been pulled out of other duties to monitor school areas. Visitors are required to ring a doorbell and show identification before they can enter. Schools have also updated surveillance systems.

The school district of Buffalo, still reeling from a deadly shooting that happened earlier this month, announced new security rules effective immediately. All visitors — parents, siblings, vendors — have to call ahead for approval. No exceptions will be made. They may be subjected to a search by a wand detector. Doors will be locked at all times.

In Florida’s Jacksonville, the chief of school police announced that backpacks or large handbags will not be permitted inside school premises for some time. Small purses will be allowed but can be searched by authorities present on-site.

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Some schools went beyond increasing security. Kingsville Independent School District announced that it will be ending its school year one week ahead of schedule, citing a discredited threat against a middle school. The school is roughly 320 kilometers southeast of Uvalde, Texas.

Two Seattle-area schools went into lockdown Friday morning and police eventually recovered an airsoft gun, Associated Press reported. The Everett, Washington, schools then had their lockdowns lifted.