(CNN) -- Jefferson Thomas was risking his well-being by leaving an African-American school for Little Rock's all-white Central High School with eight other students in 1957.
But a simple comparison of the schools' biology classes helped compel the then-15-year-old to go through with it, his sister Alma Hildreth recalled Monday, a day after Thomas died of cancer at age 67.
Thomas was one of the "Little Rock Nine" -- the nine African-American students who integrated Central High in Little Rock, Arkansas.
"In his old school, they would go to biology class and dissect a frog, but they had only one frog that all the students would dissect with the teacher," Hildreth said. "But he heard at Central, all the students had their own frog to dissect, and he wanted to go to Central High because he would be in a class where each student had their own frog."
"He found out about the wonderful education they were getting there, and that's what he wanted to experience," Hildreth, 79, of West Covina, California, said in a telephone interview.
Arkansas' governor had ordered National Guard troops to keep the nine from entering the school in September 1957, despite a federal court order desegregating schools. Two weeks later, after the court ordered the governor to stop interfering, President Eisenhower ordered soldiers to escort the children past angry protesters.
This would be just the start of the nine students' difficulties at Central. Military guards escorted them to class throughout the school year, but students still would find opportunities to spit on them, push them down stairs and hit them, Hildreth and another of Thomas' siblings said Monday.
"I do remember [the family] got a call that he had been knocked out -- someone had hit him on the back of the head while he was at a locker in a hallway," said Thomas' sister Jessie Agee, 70, of Los Angeles, California. "But he wanted to continue on with it."
When it was time to leave school and the protection of the guards, he'd run home, and one of his older brothers would wait around a corner to escort him the rest of the way, Agee said.
"His brother would wait on him ... stand at the corner and wait with a tire iron or something, and more or less dare someone to mess with him," Agee said.
The "Little Rock Nine" were selected to register with Central because of "their excellent grades and records of good behavior," according to the Little Rock Nine Foundation.
Agee was an upperclassman at Little Rock's Horace Mann High School when her brother -- the youngest of eight siblings -- entered Central as a sophomore.
"I thought it was a good idea," she said of her brother's move. "We pretty much all did, except our mother. She wasn't too keen on it, but she went along with it.
"His father wanted him to do it. [Our mother] finally gave in. Him being the youngest, she was very protective of him. And he managed to do it."
Both sisters said they were scared for their brother. "But we just prayed for his protection, and he would just say, 'This is something I was supposed to do,' " Hildreth said.
Arkansas' governor closed Little Rock's high schools to avoid integration in 1958, but they reopened the next year, and Thomas graduated from Central in 1960. He went on to serve with the U.S. Army in Vietnam and got his bachelor's degree from Los Angeles State College before becoming an accountant for the Department of Defense.
He died in Columbus, Ohio, where he had retired. He was too sick to attend a cousin's wedding and a family reunion this weekend in the Atlanta, Georgia, area, where his sisters were when they learned of his death, relatives said.
Thomas "had spent the last decade of his life doing community service, traveling to promote racial harmony and supporting young people in seeking higher education," said a statement from the Little Rock Nine Foundation. In 1999, Thomas and the other "Little Rock Nine" members received a Congressional Gold Medal from President Bill Clinton.
Thomas is survived by his wife, Mary, a son and two stepchildren, according to the foundation.
Hildreth said she believes God protected Thomas from frequent threat at Central so he could accomplish a mission that God had given him: "To stand up and do what he thought was right, [and to show] that education belonged to him and all the children."
"He did a lot of good that he really enjoyed doing and wanted to do. He did a lot of speaking and encouraging young people to reach for the stars. That was his mission, to do that," Hildreth said.
The CNN Wire staff and CNN Radio's Michelle Wright contributed to this report.