Stepping inside, the group that became known as the "Clinton 12" made the public high school in this little mill town the first to be integrated by court order in the racially segregated southern U.S. on Aug. 27, 1956.
"It was very intimidating," said Cain, now 67 and living in Nashville. "People were calling us names and things. But you had to kind of keep a stoic face and hopefully not show any fear.
"But inside," Cain said, "I was afraid."
It had only been nine months since Rosa Parks, a black woman, had refused to give up her seat on a bus in Montgomery, Alabama. It would be another year before President Dwight D. Eisenhower would send federal troops into Little Rock, Arkansas, to desegregate Central High over the governor's objections.
Tennessee Governor Frank Clement, too, would send troops into Clinton, but it was to uphold the law, not defy it, at a time when blacks still couldn't eat at the lunch counter with whites and had to watch movies from theater balconies.
"Had we not stuck it out, had we not stayed, the whole South would have been put back a few years," said Gail Ann Upton, of Sweetwater, a 15-year-old junior in 1956.
The students and the city of Clinton, which today has fewer than 10,000 people and a black population less than 3 percent, not only survived but now take pride in the story.
On Thursday, the city will premiere a 90-minute documentary titled "The Clinton 12" narrated by James Earl Jones. Two days later, civil rights pioneer Congressman John Lewis, a Georgia Democrat, and Congressman Zach Wamp, a Tennessee Republican, will mark the 50th anniversary by opening a museum devoted to the event in a former all-black, two-room elementary school.
"We just felt like we have been a footnote in history" long enough, said city manager Steve Jones, 41, noting that Arkansas' "Little Rock Nine" were honored on a postage stamp in 2005 and received congressional medals in 1998 from President Bill Clinton.
Before the integration, black students had been bused to an all-black school in Knoxville, 20 miles (30 kilometers) east. Four black students were turned away when they tried to enroll at Clinton High as early as 1950, prompting a lawsuit by a group of citizens that was later joined by the National Association for the Advancement of Colored People.
Federal Judge Robert Taylor rejected the suit in 1952, saying the education in Knoxville was as good or better than in Clinton. But Taylor reversed himself after the Supreme Court struck down the separate-but-equal foundation of Jim Crow segregation two years later in Brown v. Board of Education. In January 1956 he ordered Clinton High desegregated by that fall.
Rabble-rousers, segregationists and the national media — including CBS legend Edward R. Murrow — swept in as the black students joined Clinton High's 800 white students, and the governor had to call in 600 national guardsmen to restore order.
"I want to tell you we were nervous," said Alfred Williams, now 68. "When this school integrated, you could see the hate in people."
Jones said the museum will tell two sides of the story — the white version, which tends to portray the black-white tensions as more severe outside school than inside, and the lesser-known black version, which saw the struggle as more constant.
"When we were in class, the teachers were nice and everything was sort of smooth in there," Upton said. "But once we got in the hallways, things were pretty rough. They would step on my heels and make them bleed and pull my hair and that type of thing."
Cain said the pressures became so great he walked out of school one day.
"I just couldn't take it anymore," he said. "But my mother and father talked to me that night. They said, 'You have to go back. If you drop out, you have been defeated.' So I went back."
The unrest stemming from Taylor's order climaxed on a Sunday in October 1958, when the high school was rocked by three massive explosions. No one was hurt, but the vandalism unified the community as parents, teachers and students — black and white — worked together to fix up a building in nearby Oak Ridge as a temporary home for Clinton's integrated student body.