Wearing graduation-style cap and gown, U.S.-raised immigrant Alberto Peniche, 20, born in Mexico City and raised in Boston, waves and shouts as he and nearly three dozen youth prepare to present themselves to U.S. immigration officials as they cross the international bridge in Nuevo Laredo, Mexico, Monday, Sept. 30, 2013. Peniche’s sister Maria Ines was part of the original “Dream Nine,” a smaller group that attempted to enter the U.S. at Nogales, Arizona, in July. (AP Photo/Christopher Sherman)

LAREDO, Texas — Nearly three dozen migrants marched across the U.S.-Mexico border without papers Monday, the latest group of a younger generation brought to the U.S. illegally as children that seeks to confront head-on immigration policies they consider unjust.

Wearing a colorful array of graduation-style caps and gowns, 34 young people who spent long stretches of their childhoods in U.S. cities like Phoenix and Boston chanted “undocumented and unafraid” as they crossed the Rio Grande into Texas. Customs officials separated them from regular pedestrian traffic and the rest of their entourage before beginning lengthy interviews.

The risks born by their parents’ generation involved dangerous journeys through darkness across desert and river. The teenagers and 20-somethings who crossed Monday face what could be weeks in detention and possible deportation as part of what could be a growing form of public protest.

They follow the “Dream Nine,” a smaller group that attempted to enter the U.S. at Nogales, Arizona, in July. They requested asylum and were released after about two weeks in detention to await their turn before a judge. Monday’s contingent expected something similar.

U.S. Customs and Border Protection, whose officers determine who is admitted at the border, said privacy laws prohibited it from discussing any individual cases.

At the heart of both groups’ protest was a change to U.S. immigration regulations made in June 2012 giving something called deferred action to immigrants who were brought to the country illegally as children. Those who were in the U.S. at that time and met a list of criteria they could apply for a renewable two-year deferment and work authorization.

But the young people crossing Monday had left the U.S., either voluntarily or through deportation, months, weeks or even just days before the deferred action announcement, commonly known as DACA.

“We look at this action today and the Dream Nine as a type of extension of DACA,” said David Bennion, an immigration lawyer travelling with the group. “What we would like to see is the people who left, like these 30 who otherwise would have qualified for DACA, to have that be taken into consideration.”

There were several minors in Monday’s group, including 17-year-old Luis Enrique Rivera Lopez. He came to the border from Guasabe in Sinaloa, a Mexican state that he had known only by its reputation for drugs and violence before going there from Los Angeles early last year.

“I wanted to have a sense of my roots,” Rivera said of his decision to return to Mexico, where he hadn’t been since he was 1. “I wanted to know where I was from.” He considered studying to become a chef specializing in the seafood dishes of Sinaloa, but was forced to start high school over again in Mexico.

The experience was rewarding in some ways. He got to know both sets of grandparents. But after 19 months away he missed his parents and three siblings who remained in Los Angeles. He also found he didn’t fit in after having grown up in Los Angeles.

“When I got to Sinaloa I didn’t dress like anyone. My haircut was different. My style of walking was different. My Spanish was like way off,” he said.

David Leopold, an immigration lawyer and past president of the American Immigration Lawyers Association, said the tactic concerned him.

“The focus now should be on getting the House of Representatives to do its job and fix the immigration system,” Leopold said. “I don’t know that these actions move that issue forward.”

The group underwent detailed planning for the crossing. The participants arrived at a migrant shelter in Nuevo Laredo several days early. A series of meetings trained them on how to conduct themselves. What they wore, the order they walked in and what they carried was all determined.

Lorena Marisol Vargas, 19, left her home in Tucson, Arizona, in April 2012, less than two months before the deferred action announcement. She had travelled to Ciudad Juarez, Mexico, across the border from El Paso, Texas, to interview in the hope of getting a visa to be in the U.S. But the visa was denied and she was not permitted to return.

Vargas’ mother, a naturalized U.S. citizen, had to return to the United States without her. The teenager who had lived in the U.S. since she was 6 went to Uruapan in Michoacan state to live with relatives she hardly knew.

“To me, my home is Tucson, Arizona. I was raised there,” Vargas said.