The teachers at Frontier Middle School in Moses Lake, Washington State, wear identification badges these days. The corridors have been widened to eliminate hiding places and are monitored by surveillance cameras. Twice a year, students and teachers practise safety drills, locking doors and windows and retreating to designated rooms until the all-clear signal sounds. Guards patrol the halls. This is the outward evidence that, three years ago, two students and a teacher were shot and killed by a 15-year-old classmate.
The other signs are more difficult to see. "Sometimes I think the only people who understand are people who were in a war," says Peggy McNutt, a teacher whose son, Cory, was taken hostage by the teenage killer. He survived, while a girl who switched seats with him moments before, was fatally shot.
"It will be with him forever," Mrs McNutt says. "Some people have this mindset, act normal. You can't act normal. What happened isn't normal."
The McNutts are among a growing number of victims of American school shootings, trying to resume their lives after the violence has ended and the stories have slipped from the front pages.
Every incident brings back painful memories. The killings in Littleton, depicted on front pages and television screens around the world, are yet another chilling reminder. For some it's less than a year since they were traumatised by a series of vicious incidents.
Schools try to cope by adding so many security measures that some look more like fortresses than learning centres. Others train their staff to respond in certain ways to coded warnings of violence.
Parker Middle School in Edinboro, Pennsylvania, keeps all its doors locked during the day after teacher John Gillette was shot and killed at a school dance on April 24 last year - allegedly by Andrew Wurst, aged 14. Only the main entrance remains open. The other teachers who were chaperones at the dance meet twice a month with counsellors.
But the Columbine shootings - four days before the one-year anniversary of Mr Gillette's death - has shaken what Edinboro officials were calling their "campaign to create a new normal".
"It's a very difficult time right now," says Myra Reichart, spokeswoman for the Edinboro teachers' union. "Everybody still hasn't recovered."
Little has changed in Jonesboro, Arkansas, where last March two boys killed four girls and a teacher. "I think part of the reason is the feeling that there really wasn't anything that could have been done to prevent the shooting in the first place," says Wilma Maiers, a teachers' union spokeswoman.
In West Paducah, Kentucky, where three students were fatally shot and five injured in December 1997, families are suing 42 city, county and school officials who they say could have prevented the tragedy. Some parents in Moses Lake also have sued, forcing students such as Cory McNutt to relive the incidents when giving testimony in court.
A report from the US Government late last year insisted that schools are much safer than most people think.
In the 1993-94 school year, 52 children were killed in school violence nationwide. In this school year, two months from its end, the death toll stood at nine until last week's shootings. It now stands at 23.
Nor is the impact limited to schools which have experienced violence. The Gettysburg Area School District, near Edinboro, for example, put extra large windows into its new high school to allow teachers and administrators a broad view of students at all times. Certain areas are accessible only by using a computerised key card.
But locks and lawsuits won't prevent more violence, says Ms Reichart. "You could take all the precautions in the world and it's still possible that something like this could happen."
As for the aftermath, Ms McNutt says it's the little things, such as notes from counterparts at other schools, that matter to her son and his classmates. He also attends counselling sessions. After Littleton, she asked Cory, what helped him the most. "It was having people to talk to. He says, 'Mom, some of those kids didn't do that. And they're not doing well.'" There is still a lingering fear among Edinboro parents. Cindy Zemcik, whose son was wounded, says she still has trouble seeing him off to school every morning.
"I sent him innocently to a dance, and he almost didn't come home. I'm not sure that he will come home from school safely."
In Springfield, Oregon, two students were fatally shot and 20 hurt by a 15-year-old who also killed his parents in May last year. Thirteen of the students who lived through the shooting responded by staging a play, "Bang, Bang, You're Dead," focusing on the jail cell reflections of a teenage murderer confronted by spirits dressed in black who demand an answer to the question: "Why did you kill me?" Eventually he answers that it was because they laughed at him.
Ms McNutt says the killers are also victims. "What do we really have in place to help kids in our communities? There are things to help kids who are in trouble. But what about before that?" Schools have had a hard time keeping guns and knives outside their doors.
Many urban schools have had metal detectors at their entrances for decades; a few suburban and rural schools are now following their example. The US Department of Education says 84 per cent of public schools now limit access for security reasons. A smaller proportion use metal detectors and random searches every day.
Penalties for students caught with weapons also have been significantly strengthened - in California they can be suspended for up to a year.
And many communities now require conflict resolution training for teachers and students. Pennsylvania legislators are considering a proposal that would require it by law - President Clinton says the country must do more to reach out to its children "and teach them to express their anger and to resolve their conflicts with words, not weapons".
After Littleton, there also has been renewed criticism of animated television programmes, action movies and video games. The families of the three Kentucky victims shot at Heath High have sued the entertainment industry for inspiring their childrens' youthful killer. President Clinton has urged parents to shield their children from violent images.
Symbols that encourage violence are also being banned, including clothing with certain messages. And schools in Colorado have now banned students from wearing trench coats.