On the day of the attack at Sandy Hook Elementary School, there were fewer police officers in Montgomery County schools and fewer buzzer entrance systems in Prince George’s County schools. Fairfax County had not updated 10 decades-old, open-classroom schools that lacked individual locking doors.

Virginia lawmakers had not mandated two lockdown drills a year, and Maryland had not allocated $25 million for school safety improvements.

The indelible horror of the massacre at the Newtown, Conn., school on Dec. 14, 2012, changed all of that. The tragedy that left 20 children and six school staff members dead one year ago also left its mark on how schools think about the way they protect students. School leaders across the country have wondered how to tighten up. Lawmakers have deliberated. Parents have weighed in.

Experts say that schools remain among the safest settings for children and warn against costly or fear-driven changes that are often ineffective. In Connecticut, a recent report could not pinpoint a motive for the rampage by Adam Lanza, 20, who shot through a window near a locked school entrance just after 9:30 on a Friday morning.

In the Washington region, school leaders have ramped up security. Many have fast-tracked building improvements, such as electronic access controls. Some have staged more drills or collaborated with local law enforcement.

Prince William County has funded an additional 15 “school resource officers” — uniformed, armed police — so that one will be stationed in every county middle school and high school.

“No level of security can ever 100 percent prevent school shootings, but this is probably the best thing we can do in a relatively short period of time,” said Corey A. Stewart (R-At Large), chairman of the Prince William Board of County Supervisors, who had sought to cut such positions to save money but shifted course after Newtown.

Prince George’s has undertaken one of the region’s more extensive efforts to boost security with a $7.5 million project to install electronically controlled entrances, panic buttons and cameras at all of its schools. It also mandated systemwide lockdown drills and steered funding toward fencing around portable classroom trailers.

The county’s next step: creating a school district police force.

“With everything that happened, we wanted to make it a priority,” said Rex Barrett, Prince George’s director of school security. “We just had to look at it differently.”

Some changes driven by Sandy Hook are fully in place.

In Reston, teacher Sharon Burns was elated by the sight of the classroom doors installed last summer at her elementary school, which was built without them in an earlier era of school design. After Sandy Hook, Burns could not shake a sense of vulnerability, feeling that her first-grade class really needed a door. She started a petition.

School officials were receptive, she said. At the time, 10 such schools were not outfitted with doors, said Fred Ellis, director of safety and security for Fairfax schools. Now all have them.

With doors in place throughout the building, Burns said she feels safer. She said parents and other educators were thrilled. “I walk in with a smile every morning,” she said.

In Montgomery, the tragedy produced support for a school-based police program that was slashed amid budget pressures.

Last spring, the county doubled the number of resource officers in schools from six to 12. Other local police officers and a sheriff’s deputy work at Montgomery high schools to help fill in the gaps.

With this change and others, Montgomery County Council President Craig L. Rice (D-Upcounty) said he believes schools are safer a year after Newtown.

“We have made tremendous gains,” he said.

There are no numbers that track a national rise in school police, but Mo Canady, executive director of the National Association of School Resource Officers, said his group trained nearly 1,000 more this year than last. “I think schools in general were safe before Newtown, but I think a lot of districts have paid a lot more attention to school safety.”

In Virginia and Maryland, officials have put money aside for school security improvements. Virginia became the first state to require threat assessment teams in all public schools, aimed at reducing student conflict and lowering suspension rates. Maryland officials recently opened a Center for School Safety, a clearinghouse for school data and best practices.

With an intruder being central to the Sandy Hook tragedy, access control to schools has become a dominant issue. In Virginia, 2012 data show that controlled access systems are in place at 59 percent of elementary schools, 51 percent of middle schools and 37 percent of high schools.

In Montgomery, officials expedited funding in January for a $364,000 project to install buzz-in systems with exterior cameras and intercoms at a group of elementary schools. Bob Hellmuth, Montgomery’s director of safety and security, said there is an effort to install similar systems at middle schools and to add cameras throughout the system.

In Fairfax, elementary and middle schools have buzz-in access controls, and in the past year the district has expanded such measures at high schools. A pilot program was started before Newtown at two high schools, and the tragedy increased interest among others.

Now 13 high schools have door access systems, said Ellis, the security director.

In Alexandria, officials say they have created a full-time position for a security and emergency management specialist to focus on school security.

Loudoun officials have also focused on security practices — locking exterior doors, making sure classroom doors are in a locked position so that they can be closed easily, and training staff to screen school visitors.

School officials in Arlington County and the District did not immediately respond this week to requests for details about their security efforts since the Sandy Hook shootings.

Nationally, experts say human action is often undervalued in school security, as officials look to equipment to make schools safer.

Proven, reliable best practices are most important, said security consultant Kenneth Trump. After Sandy Hook, he said, “people have been looking for the ‘wow’ — something new, something that feels empowering, something that meets our emotional security needs, but may not actually make us more safe.”