CALDWELL -- Caldwell High School is barring students from carrying backpacks during school hours in the wake of threats that have roiled area school districts.

The new policy was announced in a post on the school's Facebook page.

Students will still be allowed to bring backpacks to school but must place them lockers upon arrival. Backpacks cannot be worn during lunch or passing periods.

Bags and purses the size of a standard piece of letter paper or smaller will still be allowed, according to Caldwell High.

"We understand this will be a transition as students and staff get used to a new procedure," the school wrote.

Students who bring athletic bags to school will be required to store them with physical education teachers. PE teachers have been made aware of the change, and are prepared to open up the locker rooms to storage.

Every student at Caldwell High will be assigned a locker on Wednesday. There are no fees required to get a locker, and there are enough available for one to be assigned to every student, the school stressed.

Caldwell High is not increasing passing periods to allow students more time to fetch books or other belongings from their lockers between classes, but the school says it will "monitor the transition" over the next several weeks and make adjustments if necessary.

The announcement came three weeks after 17 high school students were killed and more than a dozen were injured at Marjory Stoneman Douglas High School in Parkland, Fla. Treasure Valley schools, including Caldwell High, have also been the target of threats in recent weeks, alarming students, and parents.

Administrators alerted parents to graffiti involving a threat to Caldwell High on Feb. 28. Although the threat was deemed not credible, the school said it was increasing security sweeps, student supervision, and bathroom monitoring, and had turned the situation over to Caldwell police.

RELATED: One Idaho school district is using a new app that connects school staff members to local police during an emergency situation.