Dressed in fashions of 100 years ago, students at The Sidwell Friends Lower School in Bethesda launched 100 balloons with return-address tags attached in celebration of the private school's centennial last month.

To their surprise, the gray and maroon helium-filled balloons meandered--or in one case, raced--as far as Long Island.

Gail Klewicki of Old Westbury, N.Y., wrote to the second grade at Sidwell that her daughter was playing outside with a friend when they found the balloon and plastic-coated note 5 1/2 hours after it was launched on a rainy April 8.

It was the best response the children received "because we were really very surprised it got there so fast," one student said.

Thus far, they've received 20 letters, and they're still coming.

"Twenty percent is a good response," said Carol Borut, teacher of the second grade at the Quaker school.

All of the 280 students from kindergarten to fourth grade participated in the launching, and the second graders volunteered to respond to the letters.

"We got a lot of letters the first week, then there was a lull," Borut said. Now they are getting letters from "farmers plowing their fields" or people finding them in the woods and obscure places.

Besides the one that reached Long Island, others made it to New Jersey, Pennsylvania and northeastern Maryland; one was found by a former Sidwell student.

Elizabeth Derr was walking in a field near her house in Conowingo, Md., when she spotted a fallen balloon. She recognized the address because she attended eighth grade at Sidwell in 1953.

"I was tickled," Derr recalled. "It was such a coincidence."

In another coincidence, Sidwell's kindergarten teacher, Anne Batzell, recognized the name on one of the letters as a former pupil at a Philadelphia school. David Kramer wrote he was walking along the Schuylkill River in Philadelphia and his dog found the balloon.

Most of the letters were short, and Mrs. Glen Moore of Oxford, Pa., offered motherly advice: "Do your lessons well and be good to your teachers and parents."

The main celebration of the school's centennial takes place this weekend at the campus of the upper school on Wisconsin Avenue NW, but Richard Lodish, principal of the lower school, said his school has been preparing for the event with the balloon launching, building a time capsule and other activities.

The capsule, which will be buried in cement in one of the school's fields on "Grandparents' Day" tomorrow, includes a finger puppet, an alphabet book, a wishbone from a chicken dissected in a science class, ash from Mount St. Helen's volcano in Washington and a picture of Lodish at school on a camel that he rented for Halloween one year.

And the fate of the balloons that were not recovered? The second graders had some answers.

"Some of them could have landed in the Chesapeake Bay," one boy said. And, noted another student, "Sometimes dogs chew them up."