NORTH ANDOVER, Mass. -- During last month's assembly at Kittredge Elementary in North Andover, Massachusetts, the school honored three former students for their contribution to Kittredge.

The former students are Alex Gamble, Kyra Brown, and Celia DiSalvo. They all just graduated from high school, but the present they left behind when they were at Kittredge is still all anyone can talk about.

The kids started working on the gift unwittingly. It was 10 years ago. They were in second grade and out on the playground during recess when one of them saw a little rock -- or what looked like a little rock -- sticking up out of the ground.

Left to right: Alex Gamble, Kyra Brown, and Celia DiSalvo CBS News

Kyra says they found sticks and thought, "let's just dig this out of the ground."

Richard Cushing was principal during much of the excavation. He says the kids were out there every recess.

"I have to tell you, their hearts were broken when the first frost appeared because they had to stop," said Cushing.

But year after year they returned to the project. Digging mostly with sticks and plastic spoons they got from the cafeteria, the kids dug down -- through second grade, third grade, fourth grade and fifth grade -- until finally, just before moving on to middle school, they finished.

The principal brought in heavy equipment to lift it out of the hole for them. That was 2008. Now the three are like rock stars around Kittredge, partly because of the accomplishment itself, but mostly for what the rock has become.

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"It has evolved into something that we never could have imagined," said Celia.

Today, some kids say this rock has the magical power of making friends.

"It's a beacon to some of the students out there who get picked on," said a student.

"And they'd go and sit on the rock and like, by the end of recess someone will go sit with them," said another.

Walter Wanyoike CBS News

Walter Wanyoike is a firm believer in the power of the rock. He says he'll never forget it.

"I waited there and then eventually some kids came and that changed my life forever," said Walter. "When I made those friends it felt magical. I thought I would just sit there alone at recess. Then friends came by. I never thought that would happen. "

When those three started digging they say they used to wonder if one day they would eventually uncover a buried treasure of infinite value -- and now we know, they did.

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