WORCESTER - It’s a relatively simple act: marking a veteran’s grave with an American flag. But for roughly 50 Junior Reserve Officers’ Training Corps students Thursday, it was a lesson in history, responsibility, and sacrifice.

“Seeing how many people have died for our country puts into perspective how much you sacrifice going into the military,” said Carlos Perez, 18, a senior and the JROTC operations officer at South High School. “It helps you understand the sacrifices people have made for your country.”

Around 50 JROTC students from Burncoat and South High Schools joined members of American Legion East Side Post 201, Blue Star Mothers and a few private citizens Thursday to place American flags and veterans markers on veterans’ graves in the north section of St. John’s Cemetery.

“It’s very gratifying to see the kids come out,” said Larry Sasso, American Legion Post 201 commander. “When you actually come out and put a flag on a gravestone, there’s a special feeling you have. It’s not just a gravestone; it’s a veteran who was fighting for our freedom.”

The flag placing is a tradition in which the American Legion Post has been involved for approximately 60 years. But membership in the post - like in its brethren countrywide - has aged and diminished over the years, and the post officers decided to call for student reinforcements in 1997.

“As the guys got older, we had to have younger help,” said Kevin Mercadante, a post member.

“This is the future, you have to carry it on,” said Scott Laplante, finance officer and athletics officer at the Post. “These guys could be the legionnaires of tomorrow.”

So students fanned out across the cemetery Thursday morning with around 4,500 flags; replacing worn flags, adding flags to veterans’ gravestones where flags were missing, and pausing to reflect on the sacrifices that veterans made to their country.

“I try to look at all of them,” said Sebastian Lima, 16, and group commander of the JROTC at Burncoat. “Some go back to the Civil War so there’s a lot of history here.”

Mr. Lima said he was impressed by the self-reliance of the veterans whose graves he marked.

“Now we have technology to do a lot more and then they had to rely on themselves,” he said.

Mr. Perez, who said he has participated in the flag-laying each year since entering high school, said the day was an opportunity for JROTC members to understand the breadth of the program.

“It’s an opportunity for cadets to see that the program is about not just academics but helping out the community,” Mr. Perez said. “It’s an experience you need in order to become better in life.”

Alicia Quirindongo, 15, said the experience also helped the cadets bond.

“It was a pretty good time to get to know younger classmates in the unit,” Ms. Quirindongo said. “It brings our unit more together.”

And she said she was glad to participate.

“It’s an honor to change the flags for people who fought for our country and our rights,” Ms. Quirindongo said.