After a spate of violent incidents last month, officials increased police patrols inside the school and around the campus.
Three students were stabbed, one fatally, during a two-week period, prompting the district to order a review of its security procedures.
Students are no longer allowed to leave the building during the school day.
In a letter to parents, schools superintendent Brian Osborne said the recent mass shooting in Parkland, Florida, played a role in the district's decision.
"(T)he events in Florida, coming so soon after the death of New Rochelle student Valaree Schwab, have been deeply painful and distressing to me, and I know that our entire community shares strong concerns," Osborne said. "Enhancing school safety and security is ongoing. We have made major progress, and we have a long way to go to modernize and improve."
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