Under the shade of tamarind trees, the teenage students display their battle wounds.
One shows where a gunshot grazed his neck last month. Another bares two scars on his scalp and forearm from a recent knife attack.
"It happens so often we're used to it," says Atsadawut Taluechai, a skinny 18-year-old who carries a knife to school. "I've been shot in the leg and stabbed in the back."
These are the survivors of Thailand's high school gang wars. So common that the media generally ignore them, the battles were thrust into the headlines and parliamentary debate this month when a 9-year-old bystander was shot and killed.
Teachers and students say the violence is another outgrowth of the problems that affect the poorer half of Thai society, much of which feels overlooked by the government. The gap between rich and poor was highlighted by the "red shirt" anti-government protests in April and May, which some protesters called class warfare.
Gang violence has plagued Thai schools for years, mostly at the country's 835 vocational schools, which cater largely to the children of the working class: taxi drivers, security guards and factory workers. Police say there were 900 reported incidents in Bangkok in the first half of this year, but teachers say the actual number is higher.
Many of Bangkok's 106 trade schools frisk students on arrival. In recent years, the pencils and rulers that were the weapons of choice have been replaced by machetes, homemade bombs and cheap guns.
Long-running bitter rivalries between vocational schools often spill into public buses and shopping malls frequented by students. Gangs stalk bus routes taken by rival schools, and commuters have long complained of the dangers of riding buses near vocational schools.
That risk was highlighted on Sept. 1, when students opened fire on a public bus in Bangkok. Four stray bullets hit the 9-year-old boy, shaking parents and educators. Principals from high-risk schools were called to Parliament twice for sessions on how to stop the violence.
Here in Lopburi is the government's proposed solution: A rural retreat for gang leaders.
Last weekend, 105 of Bangkok's most-renowned troublemakers were bused two hours to the countryside to eat, pray and camp with their enemies.
"This is the first time we've brought the key leaders together," said Lerpong Watcharamai, the retreat's organizer and a trade school deputy principal. "These are the students with the power to influence the rest."
The rules for the retreat: No mobile phones, no sunglasses, no weapons. The students were searched on arrival at the Ba Sak Campground, a sprawling center with 30-bed dormitories and grassy fields set amid tamarind and frangipani trees.
Sixteen soldiers from the army's First Psychology Unit mixed boot camp drills with icebreaking activities, including song-and-dance numbers in which officers and gang leaders swiveled their hips and sang crude songs.
One exercise, holding hands and bowing to each other, met some resistance.
Next came group meditation before a Buddhist altar. "Put your mind to rest," a soothing voice said over loudspeakers, as the gang leaders lowered their gaze and sat cross-legged on the floor. "All the confusion and turbulence in your mind, put it away."
The students wore matching white T-shirts printed with the slogan, "Reconciliation. Learn to Love. Unity." Most didn't fit the image of an inner-city thug. Fresh-faced with trim haircuts, they were polite and answered questions thoughtfully.
Few saw an end to the violence. In many cases, spotting a rival school's badge on a belt buckle is enough to spark a fight.
"The problem is almost a tradition. It's been passed down from generation to generation," said Issara Kummin, 17, the student with scars on his scalp and forearm. He got them in June, he said, when 20 kids jumped him as he stepped off a bus.
He considers himself lucky: One of his friends was shot and killed in February while getting off a bus.
"I want revenge," he said, softly. "We're seen as the bad guys. But people don't know what we're up against. If we don't fight, we'll be killed."
A 16-year-old student at the Bangkapi School of Technology has been arrested for the killing of the boy on the bus. He allegedly fired the shots about 6:30 a.m. after an all-night booze binge. He reportedly told police his handgun cost 2,000 baht ($65).
"I've been here 20 years, I never thought I would see that," said Somsak Karparyoon, a gym teacher at Bangkapi, which sits amid Bangkok's northeastern industrial sprawl.
He walks the school grounds with a thin bamboo cane to whack students who arrive late, cut class or have their shirts untucked. Asked how often he uses it, he laughed and said, "Very often."
Teachers at the school escort students to and from the nearby bus stop and search the surrounding streets for hidden weapons. Trade schools in the area have staggered hours, so students will be less likely to cross paths. Riding the bus remains the most dangerous part of the day.
"You can't ever doze off on the bus. It's too risky," said Watcharin Khusuwan an 18-year-old junior studying auto mechanics at Bangkapi.
"I can't remember how many times my bus has been attacked. So many times," he said. He glanced at his watch and apologized. School had ended 15 minutes earlier, and he was wearing his school uniform. "I'm sorry. I have to leave. It's getting risky to be outside."
Associated Press Writer Thanyarat Doksone contributed to this report.