In a statement issued after the protest on Thursday at Morton West High School in Berwyn, a working-class suburb just west of Chicago, the district superintendent, Ben Nowakowski, said the school’s reaction had to do only with the interruption of the school day, not with the students expressing themselves.

The administration “did not say that the students could not protest,” Dr. Nowakowski’s statement said. “Rather, we asked that the students simply move their protest to an area of the school that would not disrupt the ability of the other 3,400-plus students at Morton West to proceed with their normal school day.”

Dr. Nowakowski did not return repeated calls seeking comment Tuesday.

But several students said the protesters, whose numbers had dwindled to about 25, obeyed the administration’s request to move from a high-traffic area in the cafeteria to a less-crowded hall near the principal’s office. There, they intertwined arms, sang along to an acoustic guitar and talked about how the war was affecting the world, said Matt Heffernan, a junior who took part.

“We agreed to move to another side of the building,” Matt said. “We also made a deal that if we moved there, there would be no disciplinary action taken upon us.”

Matt said the group had been told that the most severe punishment would be a Saturday detention for cutting class that day.

Police officers were on the scene, and Berwyn’s police chief, William Kushner, said no arrests were made. “It was all very peaceful and orderly,” he said.

But at the end of the school day, Matt said, Dr. Nowakowski gave the remaining protesters disciplinary notices stating that they had engaged in mob action, that they were suspended for 10 days and that they faced expulsion.

“I was shocked,” said Matt, 16. “We had the sit-in. So I had mixed feelings of confidence — of a job well done — and fright, because my whole educational future is at risk.”

School officials also sent a letter to the parents of all the school’s students calling the protest “gross disobedience” and reminding parents that any disruption to the educational process could lead to expulsion.

On Tuesday, a group of parents went to the school to demand that their children be allowed return to classes. At most, the parents said, the protesters’ behavior amounted to loitering, which should be punishable by detention or a meeting with a guidance counselor.

The parents have also asked that the district provide the students with some way to express themselves about issues like the war.

“Who’s the next group to go off to war?” said Adam Szwarek, whose 16-year-old son, Adam, faces expulsion. “These kids. The kids do a peaceful sit-in and they’re threatened with expulsion, yet the military’s running around the school trying to recruit.”

Parents also complained that deans, teachers and coaches singled out certain athletes and honor students and persuaded them to drop out of the protest.

Rita Maniotis, president of the school’s parent-teacher organization, said the school called her husband to say that their daughter, Barbara, a junior, was participating in the protest and that he should come to get her. He did so, and she was suspended for five days. But other parents were not called and not able to intervene, Ms. Maniotis said. “There’s no rhyme or reason to the punishment doled out,” she said.

The executive director of the A.C.L.U. of Illinois, Colleen K. Connell, said she could not comment on the case because her organization was investigating to determine whether it will take it up. In general, public school students have constitutional rights, she said, but they can be limited in a school setting.