The Beacon School students’ trips to Cuba started in 2000 and top administrators, including a teacher who has become assistant principal and a college counselor, have acted as chaperones.

The students’ six visits to the island nation are under scrutiny by the special commissioner of investigation for the New York City school system, Richard Condon, following the disclosure last month that they were unauthorized. At least two visits appear to have been illegal, and five others could have been illegal if proper permits weren’t acquired.

Several recent Beacon School graduates said in interviews that the trips also highlighted a sense of frustration with what they described as a biased presentation of history in some classrooms at the public school on the Upper West Side of Manhattan.

A 2004 graduate of Beacon, David Goodman, dismissed claims that the teacher who took students to Cuba this year, Nathan Turner, was anti-American, but said he taught history with a “Howard Zinn kind of look at the world.”

“He is off the charts liberal,” Mr. Goodman, who said he has liberal views, said. “A lot of the school is like that. I came out of there feeling that it was too leftist and they weren’t giving you enough of a general history.”

On the latest trip, the group was stopped by customs agents in the Bahamas, but it wasn’t the first time that members of the school were warned about traveling to the island country without a permit from the government.

In May 2001, the school’s current assistant principal, Harry Streep III, was interviewed by customs officials in Houston after a student was stopped because her passport contained a stamp from Cuba. According to a source familiar with the trip, Mr. Streep, who is actress Meryl Streep’s brother, was given a warning not to violate the rules of the American embargo of Cuba.

Most American visitors to Cuba have their visas stamped instead of their passports to prevent trouble later on with customs.

Speaking through a spokesman for the Department of Education, Mr. Streep denied he was admonished for traveling to Cuba. He declined to answer other questions for this article.

Only college students attending programs that last more than 10 weeks are allowed to visit Cuba as of 2004, which was the last time the laws preventing most Americans from traveling to Cuba were tightened. Beacon students have visited Cuba twice since then.

Even before 2004, travel by high school students was restricted to those that had properly received permits from the Treasury Department. School administrators and Department of Education officials declined to confirm whether permits had been acquired or answer other questions for this story because the investigation is ongoing.

Students have to fill out an application that includes an essay to go on trips abroad. Before leaving, they attend a class where they go over the country’s history and improve their language skills, students said. In some cases, the school would help defray the costs for students who couldn’t afford the full fare.

Violating the embargo of Cuba can result in a warning letter or up to $65,000 in fines, according to the Department of Treasury, which through a spokeswoman declined to comment on its investigations.

Beacon’s principal and co-founder, Ruth Lacey, denied knowledge of this April’s trip, according to published reports. She told the New York Post that the previous six visits had been approved by the city, a claim that an education department spokesman, David Cantor, said wasn’t true. Ms. Lacey did not return messages yesterday.

Students said the trips, including last month’s, were advertised on bulletin boards, announced on the intercom system, discussed in class, and memorialized in the yearbook. A review of the Beacon School’s Web site discloses notices about deadlines for applying to the 2007 trip, as well as the previous six trips.

“They were having a controversy in 2001 or 2002,” a 2003 graduate of the school, Julian Goldstein, 22, said. “It was just from going in general because it was illegal.”

Besides the history teacher who led the most recent trip, several administrators and faculty members have led trips in previous years. A history teacher and contact person for the school’s Academic Standards Committee, Bayard Faithfull, led the first trip in 2000. The college counselor, Stephanie Binder, was a chaperone in 2004 along with a history teacher and professional development school coordinator, Geoffrey Hunt.

Mr. Hunt declined to comment. The other teachers did not respond to messages yesterday.

A 2006 graduate of the Beacon School, Dantel Ruiz, 18, said she wasn’t surprised when she learned that her old history teacher, Mr. Turner, was at the center of the controversy about the most recent trips to Cuba.

“He tied Cuba into anything,” she said. “It was his example for everything and how” the American government “was fascist.”

She said pictures of Fidel Castro and Che Guevara were on the walls of his basement classroom.

Visits to other countries are an important part of the curriculum, according to the Beacon School’s Web site. Besides Cuba, students have visited France, Spain, South Africa, Mexico, and Venezuela.

A 2000 graduate of the Beacon School, a member of the first “Beacon Delegation to Cuba,” Pavel Vasquez, said the visit was part of the school’s mission to “see the different sides of everything, from science to philosophy.”

“It was beautiful and so different,” Mr. Vasquez said. “It was void of racism. When I came back here and saw a homeless person, I was in shock.

They also visited a local communist league at a school, he said.

Several students contacted described Mr. Turner as a well-liked teacher who seemed to genuinely care about whether a student learned something new.

“He focuses on things that you don’t normally focus on,” a recent graduate who went to Venezuela with him on a school trip, Sylvia Questa, 18, said. After the class. “you are able to question things that you thought were just the way it was.”