The gang leaders called the students "paros," or gang associates, and they gradually mentored the teenagers who could be trusted. They would be upgraded to a "chequeo," and from there, perhaps after committing a murder or other crime, they would be initiated as a "homeboy."
As part of their initiation rite, they would be beaten by fellow gang members for 13 seconds, as homage to the name of their gang.
That alarming ladder of recruitment into the violent MS-13 gang was revealed Friday in a 64-page indictment that said the gang found its members among young, vulnerable teenagers — some as young as 14, and many of them immigrants or the children of immigrants — at high schools in East Boston, Chelsea, and Everett.
The indictment — accusing 56 people of murder, drug dealing, and other crimes — reinforced the fear of violence among some parents and young people in East Boston and other immigrant communities.
East Boston High School student Selvin Diaz, 16, said he knows that members of the notoriously violent MS-13 gang were in his neighborhood. He pointed down the block to a house that once had a sign with the gang's colors: blue and white.
"I don't quite feel safe," added classmate Melissa Gutierrez, a sophomore. "When I hear about them, it's kind of creepy, but we just have to stay away."
Harold Shaw, special agent in charge for the Boston field division of the FBI, said high-school- and middle-school-age students were recruited to "commit the most violent acts on behalf of the gang."
The arrests linked the gang to five murders, including the killings of three teenagers in East Boston: Wilson Martinez, 15, and Irvin de Paz, 15, who were killed in September, and Cristofer Perez-De La Cruz, 16, who was killed earlier this month.
"It's terrible — we're talking about 15- and 16-year-olds who should be in school or living a full life," Boston Police Commissioner William B. Evans said.
Gutierrez, the East Boston High sophomore, said students believed the killings were gang-related, even if they didn't know the details.
"It was all in the same area, and it definitely made us feel unsafe," she said.
Though some students and parents were pleased to hear about the arrests, some said fear remained.
Nicole Zepeda, a student at East Boston High School, said she didn't think the arrests would be enough.
"It's obvious there's a lot more going on in the city," Zepeda said. "It's not the only gang in the city, and obviously you can't put a stop to it that easily."
Cindy Powell said her 17-year-old daughter has had to run from gunfire and now does not want to stay in East Boston.
"They're seeing the recent violence, and I don't want them to think this is something they should get used to," Powell said of her children.
A woman who declined to give her name because she fears retaliation told the Globe that her daughter had to change high schools after students began inquiring about what neighborhood she lived in, leading the family to become concerned about her safety.
"I asked her not to say where she is from," the woman said she told her daughter.
While Everett and Chelsea school officials said they saw no evidence of gang recruitment inside the schools, and Chelsea officials said violence was down at the high school, law enforcement officials reiterated that schools should be safe places for students.
"Schools are a safe environment for learning, and gang activity has no place in schools," Chelsea Police Chief Brian Kyes said.
"We're going to make sure that our city and streets are safe as well as our schools."
US Attorney Carmen Ortiz said the revelation about MS-13 recruiting at high schools should send a message to community members and school officials who must do more to raise awareness and create prevention programs for at-risk youth, many of whom identify with the Central American gang members.
"It is incumbent upon us to provide them with healthy alternatives," Ortiz said. "We also need to provide our schools with the training and resources necessary to counter the recruitment that gangs engage in and provide students with a safe and healthy environment in which they can learn and they can grow."
Evans said there will be counselors and school police on hand to provide alternatives for students being pressured to join gangs.
Lucy Pineda, executive director of Latinos United in Massachusetts, an Everett-based nonprofit, said her phone exploded Friday morning with calls from distraught parents. One said her son was arrested. Others recognized those arrested as friends of their children.
"The schools should have more programs," Pineda said. "And they should share these programs with organizations like ours because we're the ones who receive the complaints about the needs for our community. . . . We can educate the parents."
"It's very important that we know each other better," she said. "Who are our friends? Who are the friends of our children?"