Fresh white paint covers the soot from the fire that criminals set in the middle school principal's office in a rough Acapulco neighborhood, where gang-linked violence interrupted classes for weeks.
Outside, four stone-faced Mexican soldiers guard the gate, wielding assault rifles as big as a kindergartner to deter any more attacks.
The army arrived here and in more than 100 other schools in the Pacific resort's gang-ridden periphery three weeks ago to counter a rash of murders, kidnappings and extortion against teachers.
The unprecedented deployment of 1,000 troops to schools and surrounding neighborhoods was the only way to convince frightened teachers to return to classrooms, ending a two-month strike over the violence that had left 31,000 students homebound since November.
"We never thought it would get to such an extreme point, to be working with soldiers," said Maria Ines Aparicio, principal of the Escuela Secundaria 100 middle school.
Standing next to a burned bookshelf as children in white shirts and plaid pants and skirts waited for the final bell in the courtyard, she lamented that crime fears caused the parents of six children to leave this year.
The teachers were already on strike when assailants sneaked into the school in December and set her office on fire, incinerating documents, computers and desks. An ominous note was left with a warning: "Don't close the school."
Aparicio said she did not know why her office was attacked.
But authorities accuse one of Acapulco's gangs of setting the fire to scare teachers into paying them.
The criminals also fired bullets at a primary school and set another fire at a technical education facility, authorities say.
The National Security Commission said federal forces captured the gang's alleged leader, Ronaldo Mendoza Matilde, earlier this month in Mexicali, near the US border. Three henchmen were arrested in Acapulco last week.
- Unprecedented deployment -
It has been a tough year for teachers in Acapulco, with 21 of them murdered and around 10 kidnapped in 2014, said Alfredo Miranda, the Guerrero state education department's local representative.
Miranda told AFP that criminals left messages at schools demanding that teachers fork over their three-month winter bonus.
The assault on teachers is another black eye for Acapulco, which has lost its luster of decades ago, when it was a playground for Hollywood stars.
The city is drawing fewer foreign tourists, while drug gangs have turned it into Mexico's murder capital.
Its home state, Guerrero, has been the scene of violent protests over the disappearance, and presumed massacre, of 43 college students by a gang in league with corrupt police.
An eight-month strike by Acapulco's municipal police has added to the city's chaos.
Guerrero's education secretary, Salvador Martinez Della Rocca, said hiring private security for schools would have been too expensive, so the military was called in.
"It's an unprecedented event in the history of my country for soldiers to be guarding schools, but there was no other way," Martinez said.
"Organized crime was inside the classrooms. They corrupt children, sell drugs through them, get information about teachers, make them do the work of any criminal."
Martinez plans to add protective walls around schools, put up surveillance cameras and install panic buttons to alert police. The troops will remain until the gangs are rooted out, he said.
Teachers, parents and students say the military presence makes them feel safer, but that it should have never come to this.
Jesus, a 16-year-old student at the Secundaria 100 middle school, remembered the panic in the classroom when shots were heard outside last year.
"The teacher said, 'keep calm,'" recalled Jesus, a tall kid with earphones dangling from his shirt's collar. "The situation is better now, because it used to be critical."
A science teacher, Amalio Hernandez Dimas, said someone posing as a parent had come up to him outside a classroom last year and threatened to abduct him, saying "If you don't behave, we're going to take you away."
Another teacher's car was stolen in front of the school.
"This is considered a high danger zone," Hernandez said.
- Fears remain -
While the military deployment has reassured parents and teachers, many say they also need more security in their neighborhoods.
Ramiro Villa Salas, principal at the 79 Technical school along a dusty road near the airport, said his facility had closed on November 27 after an administrative assistant and her three-year-old daughter were kidnapped as they walked home last year.
They were later freed, but he said the violence in the area led parents of 25 children to remove their kids from the school.
"We arrive at 7:00 am and leave at 2:10 pm. The issue is the commute home. That's where we feel afraid," Villa Salas said.
Other teachers and parents are concerned that the presence of soldiers could attract more trouble.
"On the one hand we feel more at peace, but on the other hand we are nervous at times, that something will happen because they are here," said dressmaker Hugo Estrada, as his 13-year-old daughter entered the Tecnica 5 middle school, which suffered an arson attack last year.