WASHINGTON (NYTIMES) - Just hours after a gunman killed 10 people at a Texas high school, two students 1,000 miles (1,609km) way worried about the safety of their usual seats in the school cafeteria.

Calysta Wilson and Courtney Fletcher, both juniors at Mount Pleasant Community High School in Iowa, believe their table in the cafeteria would be the first one a gunman entering the room would target.

"We sit at the table closest to the doors," Calysta, 17, said as she took in a softball game. "In the case that you came in as a shooter and you killed the first person you saw, I would die. I would not make it."

It is an unnerving, new consideration born from the grim, steady beat of mass shootings across the country - the last two 93 days apart on high school campuses in Florida and Texas.

As the reality of school violence sinks in, the conversations among many high school students have changed from "This could never happen here" to "What do we do when this happens?"

Students raised with the persistence of mass shootings and versed in the protocol of active shooter drills, now think often of the possibility of a shooting in their schools. Whether they are in English or history class, they routinely consider the safety of their classrooms, even running scenarios in their heads about how likely they are to get shot.

Since the Sandy Hook Elementary School mass shooting nearly six years ago in Newtown, Connecticut - when current high school students were of middle-school age or younger - there have been more than 200 school shootings nationwide, including the recent rampage in Parkland, Florida, which inspired a youth-led movement to reform gun laws.

Shootings are so common that students talk in frighteningly practical terms about the location of doors and windows in their classrooms as risk factors. They calculate escape routes. And they ponder hiding spots in wide-open rooms.

"It's like the front lines of a war," said Emily Rubinstein, a sophomore at a New York high school. "Being seated in front of the classroom could be what makes you live and what makes you die."

Emily has given a great deal of thought to her safety as she moves through her school day. She considers her English classroom the safest. It has just one door, and it is down a hallway that makes it hard to find. Also, the room has an unusual cutout corner, with no desks in it. That would be one of the best places to hide if someone started shooting at Stuyvesant High School, in lower Manhattan.

Mathematics class is where she is most exposed. She sits in the second desk of the second row, in a direct diagonal path from the door. On lockdown drills, she has learnt that the safest place to be is pressed up against the wall where the door is, so that if a shooter looks into the room, it will appear empty. But in maths class, she has calculated that her chances of reaching that position are low.

"I sit really, really close to the door," she said. "If someone came running down the hall with a gun, I wouldn't have time."

Still, Emily said those plans have not affected her schoolwork, friendships or her extracurricular activities. "We have all these thoughts. But there's still part of my mind that's like, 'No, it couldn't happen to me.'"

Many schools have decided that it could. A 2016 report from the US Government Accountability Office found that two-thirds of school districts conduct exercises to prepare for an active shooter.

Bartlesville High School, an hour north of Tulsa, Oklahoma, has regularly held safety drills and lockdowns since 2012, when a student was arrested for making a threat against the school. In Martinsburg, West Virginia, Spring Mills High School held a "code red" lockdown this year without telling some teachers the event was just a drill, to make sure the staff was truly prepared.

And with Sandy Hook a searing memory, even elementary schools are bracing for attack. At West Greene Elementary in rural Snow Hill, North Carolina, the county will soon install locking doors in the cafeteria, just in case students and teachers ever have to hide there.

In response to the early morning ambush at a high school in Santa Fe, Texas, last Friday, L lieutenant-governor Dan Patrick suggested that schools be redesigned with fewer doors. Had the high school had a single entrance, Mr Patrick said, the gunman might have been stopped.

Mr Patrick, a Republican, quickly drew criticism from some who said he had minimised the role guns played in the attack.

Some students are no longer shocked when they hear of a shooting, considering it simply a tragic part of growing up. A gunman will walk into a high school somewhere in America, and open fire.

On the front steps of Roosevelt High School in Seattle on Saturday morning, pregame excitement for a soccer match was in the air. But when students were asked about the latest school shootings, the environment in their school and the potential for violence, the laughter stopped. Voices fell to sombre silence.

"At this point it's just kind of a reality," said William Neffner, a 17-year-old junior who plays midfield on the team. The once-a-month lockdown drills the school conducts, he said, have become routine, as have the conversations at home about what to do or not do if a gunman arrived on campus.

"It doesn't make it more likely," William said of the drills and conversations. "But it prepares you."

For the students of Marjory Stoneman Douglas High School in Parkland, who lost 17 classmates and teachers just three months ago, the Santa Fe shooting set off waves of emotions: sorrow, fear and a knowing feeling.

Eden Hebron, 14, had just finished her AP human geography test when she learnt of the early morning attack. Texts messages quickly followed.

"I read the details - 10 people - and it just broke my heart," said Eden, who was in a classroom at Stoneman Douglas where three students died. "I know the grief and emptiness they are going through knowing their friends were murdered. I know what it feels like to watch your friend die. No child should ever have to experience this."