IOWA CITY — The air felt leaden in the hallways at West High School on the morning after Election Day. The usual clatter from the building’s 2,000 students was muffled. At lunchtime, Lujayn Hamad was in the cafeteria when she said a boy she barely knew roughly bumped into her and swore at her.

“Go back home,” he told Ms. Hamad, who is 15, and an American citizen, and wears a hijab.

The comment, overheard by a friend at Ms. Hamad’s side — though denied by the male student — set off a turbulent week of tears, fury and demonstrations at West High, a large public school in this university town, which prides itself on its openness and progressivism. Minorities make up nearly 40 percent of the student body at West High, a far more diverse mix than the typical Iowan school.

In the hours and days after Ms. Hamad’s encounter in the cafeteria, similar incidents followed, students said. One girl said she was surrounded by heckling students and called a terrorist. Another said she saw people chanting “Trump” in the hallways when they passed black students. In one classroom, a student noted the absence of a Latino classmate and announced to the others, “I wonder if she got deported.”

Like many other schools around the country since the election, West High has become a microcosm of the United States itself, a place roiled by tension, divisions and mistrust. Students in many schools say supporters of Donald J. Trump have felt empowered to lash out at minorities, while outraged backers of Hillary Clinton have been spurred to organize and demonstrate. And teachers have been struggling to provide guidance even as they themselves are processing the election results.