It used to be a “lockdown” referred only to prisons.

But when Wilson Gillespie hears the word, he thinks of his own elementary school.

“A lockdown is if somebody suspicious comes up to our building, we pretend that we are not there,” said Wilson, 9, a fourth-grader at Horace Mann School in St. Paul. “So we shut all the blinds, and we lock all the doors. And we sit somewhere where we cannot be seen if you look through any part of the door or the window.”

The lockdown drills, now mandated statewide, are scary, Wilson said.

“Because sometimes they don’t announce that they’re doing one,” Wilson said. “They just do it out of the blue, so we don’t know if it could be real or not.”

As school officials and police respond to incidents of threats, shootings and other violence, the concept of campus lockdowns has become as familiar to students as blue book exams and tater-tot casserole.

“Since Columbine, there’s been growing awareness of the need to do something about this,” said state Sen. John Marty, DFL-Roseville, who sponsored the 2006 bill to mandate five annual lockdown drills in schools. “It was not something we thought about in the past.”

St. Paul College was locked down for four hours Wednesday after a student reported that she saw an armed man in an elevator who looked upset. Police believed her. Up to 3,000 students at the technical school were forced to stay in their classrooms, and then on campus, while officers searched for a suspect.

Police have made no arrests, but an investigation continues, said department spokesman Sgt. Paul Schnell.

Schnell said that since Columbine — the 1999 massacre at a Colorado high school in which two students killed 12 fellow students and a teacher — and other school shootings, law enforcement has changed its approach to situations in which a suspect is inside a school.

“In the past, when there were school-based incidents with active shooting going on, our strategy was to contain the situation,” Schnell said.

Now, he said, police go in after the suspect — rather than try to negotiate.

“In cases where there is a large number of people, the risk is too great,” he said.

The Stillwater area school district recently spent about $1.4 million to upgrade school security.

Ray Queener, assistant superintendent for business and administrative services, said the money went toward new security cameras at main entrances of all the schools, extra cameras at larger buildings, badge access to outside doors and rekeying of virtually all other doors, including classroom doors.

The badge access is a significant improvement, he said, because the doors can be controlled remotely via computer — from inside the school or at the district office — if a threat arises. The newer system also solves the problem of lost or misplaced keys that might fall into the wrong hands.

“We can disable the badge within seconds,” Queener said.

At St. Paul Public Schools, officials instruct staff to prepare for two types of lockdown: “with warning” and “with intruder,” said Laura Olson, manager of security and emergency management for the district.

The lockdown with warning might be called when an incident outside puts a school on alert or a medical situation makes it necessary to keep traffic out of the hallways.

In April, Crossroads Elementary had a lockdown as police searched for two masked men who fired shots in a nearby parking lot after holding up a gas station. The station was about three blocks from Crossroads. The robbers never approached the school. No one was injured by the gunfire.

Classes would continue as usual in that type of situation, Olson said.

If there were a suspicious intruder, teachers would lock classroom doors, draw the blinds, shut off the lights and keep the children quiet, Olson said.

More likely situations might include a mercury spill at school or a hazardous-materials incident along a rail line nearby, Olson said. The possibility of a shooter actually entering a building with the intention of hurting people is “minute,” she said.

Still, threats do crop up — and the most difficult step may be determining how serious they are, said Schnell of the St. Paul police.

A student may get angry and say, ” ‘Somebody should come in and shoot up the school,’ ” Schnell said. “That’s very different from ‘I saw a gun in the school.’ ”

But his colleagues would rather be criticized for over-reacting than see someone get hurt and have the public say, “Why didn’t you do more?” Schnell said.

Emily Gurnon can be reached at 651-228-5522.

MINNESOTA SCHOOL SHOOTINGS

October 1966: A 14-year-old student is shot and a school administrator fatally wounded by a 15-year-old boy outside Grand Rapids High School.

February 1993: A 12-year-old girl is shot and wounded by a 13-year-old boy at Sanford Middle School in Minneapolis.

October 1994: Two students are shot and wounded just outside Harding High School’s north doors in St. Paul.

November 1995: A Minneapolis North High School wrestler is shot and wounded in the school’s parking lot.

September 1997: A police officer is wounded when grazed by a bullet during a confrontation with an armed 16-year-old at Le Sueur-Henderson High School.

October 2000: Two former students are shot and wounded outside a homecoming dance at Minneapolis North High School.

September 2003: Two students, ages 14 and 17, are shot and killed by a 15-year-old student inside Rocori High School in Cold Spring.

March 2005: A student opens fire at Red Lake High School in Red Lake, killing seven — a teacher, a security guard and five students — at the school before killing himself. More than a dozen are injured. The suspect is linked to the shooting deaths of two others before he headed to the school.

February 2006: A student with a BB gun accidentally shoots a fellow student in the eye during a class at Highland Park Junior High in St. Paul.