The result is a school that mixes students of relatively modest means with extremely wealthy ones, including in recent years the children of Leon Black, a private equity investor, and Gerald D. Hines, the founder of one of the world’s largest real estate firms, among many others. In interviews, some students mentioned the Instagram feed of Michael Hess, a member of the class of 2013, who has posted photographs of Mick Jagger close-up in concert, courtside seats at a Knicks game and stops on his trips around the world.

Many Harvard business students and readers were especially troubled by Section X, and the idea that even within the extremely elite confines of one of the nation’s premier business schools, the ultrawealthy are segregating themselves.

“There is this underbelly at H.B.S. of extremely wealthy individuals — spoiler alert, I am not one of them,” said Brooke Boyarsky, who delivered a triumphant speech at graduation about social change at the school.

According to students, the members are mostly male and mostly international students from South America, the Middle East and Asia. They organize “the real parties, the parties where it’s a really limited list, the extravagant vacations — I mean really extravagant,” she said. (No students interviewed admitted to being members of the group, though some said they had attended its parties.)

“More than once I heard that ‘the only middle-class students here are the Americans,'” another recent graduate said.

Even though Section X is hard to pin down — some students said they did not believe it existed at all — it causes enormous resentment on campus, starting with its name. Every Harvard Business School class is organized into 10 sections labeled A through J, and the name Section X implies a pulling away from the wider community.

“The Section X dynamics really deteriorate the section togetherness,” said Kate Lewis, a 2013 graduate who edited the school newspaper. By the end of this academic year, Section X had become an adjective on campus for anything exclusive and moneyed, with one student talking about a “mini Section X dynamic” within her real section.