They came with notecards, highlighters and cogent arguments. And their muggy classroom transformed into a courtroom.

Advanced Placement U.S. Government students at Frederick Douglass High School in Upper Marlboro, Md., spent one morning this week in moot court, a simulation that law students use to practice delivering arguments.

The teenagers, ahead of Constitution Day this past Tuesday, took on the roles of judges and attorneys while examining Maryland-National Capital Park and Planning Commission v. American Humanist Association — better known as the Bladensburg Peace Cross case.

The case involving a 40-foot-tall, 94-year-old, granite-and-concrete cross hits close to home for the students. It unfolded about a 30-minute car ride away from the suburban high school.

The cross was built on city-owned property in Bladensburg, Md., as a memorial for 49 World War I soldiers from Prince George’s County. The state took it over in 1961.

The legal battle began when the American Humanist Association accused the state government of unconstitutionally endorsing Christianity with the cross. The nonprofit atheist organization has filed similar lawsuits in other states.

The case in Maryland moved through lower courts, and the Supreme Court agreed to hear it in February.

Tessa Guarracino, who teaches the government class at Douglass High, said she was impressed with the way her students handled the case.

“I was very proud at how into it they got,” she said. “I don’t know if a lot of 14- and 15-year-olds can say they are passionate about constitutional law.”

The students spent the weekend researching the case and preparing their arguments. Guarracino’s preparation started before, in July, at a two-day training session by Street Law — a legal education nonprofit group founded by Georgetown University law students in 1972.

“Several law students had the idea that they could teach D.C. high school students about the law and that would help some people avoid legal problems,” said Lee Arbetman, the group’s executive director. “In a democracy, it doesn’t make sense for only lawyers to know about the law.”

What started as a local initiative has grown into an operation with programming in 49 states and 45 countries. In its early days, Street Law deployed lawyers to schools to teach law lessons. Now, high school teachers — such as Guarracino — do the work, too.

Guarracino directed her class of 35 students to split into groups of three — one judge for every two attorneys. Guarracino served as a judge, too.

Each student attorney responded to questions from the judge, scribbled notes while the opposition spoke and delivered a rebuttal.

“This is very similar to the way real lawyers argue in front of the Supreme Court,” Guarracino told the class.

Davon Chapman, 15, said the exercise solidified his interest in becoming a lawyer.

“It’s strengthened my abilities to make persuasive arguments and be more versatile when it comes to knowing about the community,” he said.

To prepare, the teenagers studied the establishment clause of the First Amendment, which prevents the federal government and states from setting up houses of worship or passing laws that favor one religion over another.

Then, they brought in legal precedent from similar cases to construct their arguments.

Every student attorney was instructed to defend the state or the American Humanist Association. The assignments did not always align with the students’ personal views.

“This case makes you have an open mind to everyone’s perspective and everyone’s beliefs,” said Kayln Stanford, 15.

Khandi Walker, 15, said the exercise challenged her biases.

In June, the Supreme Court in a 7-to-2 ruling upheld the cross display and rejected the humanists’ argument that the monument represented a religious endorsement.

Justice Samuel A. Alito Jr. wrote the majority opinion, saying the Bladensburg cross is more than a symbol of Christianity.

“The fact that the cross is undoubtedly a Christian symbol should not blind one to everything else that the Bladensburg Cross has come to represent: a symbolic resting place for ancestors who never returned home, a place for the community to gather and honor all veterans and their sacrifices for this nation, and a historical landmark,” Alito wrote.

Alito was joined by Chief Justice John G. Roberts Jr. and Justices Clarence Thomas, Stephen G. Breyer, Elena Kagan, Neil M. Gorsuch and Brett M. Kavanaugh.

Justice Ruth Bader Ginsburg wrote in her dissenting opinion that the government’s maintenance of the cross has the same effect as endorsing Christianity. Justice Sonia Sotomayor also dissented.

The monument continues to tower over a busy intersection on a highway about a mile northeast of the border line separating Maryland and the District.

Most of the judges in Guarracino’s class sided with the two dissenters on the Supreme Court. The students suggested the state of Maryland substitute the cross with something secular, like a plaque or a statue of a soldier.

Jamia Handon, 15, said she did not expect the Supreme Court to rule the way it did.

“I was surprised,” she said. “But you have to remember, this country is very diverse in what people believe in.”