In 1883, 11 pupils signed up for the first class at Thomas W. Sidwell's school in the old Quaker Meeting House on I Street, a short distance from the White House.

One hundred years later, some of the Sidwell Friends School's one thousand students and several hundred alumni gathered for a "centennial weekend" at the school's spacious campus, which moved to 3825 Wisconsin Ave. NW in 1923. The event celebrated what keynote speaker Dr. Hannah Holborn Gray, president of University of Chicago and a former Sidwell student, called "the strength and vitality of this community of teaching and learning."

In its first century, Sidwell has become one of the most prestigious private schools in the country, selected by Quakers and non-Quakers for the distinctive blend of academic excellence and emphasis on reflective and communal values.

"I know it is a cliche, but it is true that the time I spent here broadened my horizons and taught me about the diversity of the world," Gray said.

The thought was echoed by students and alumni visiting the schools' modern campus. "The school didn't compartmentalize, it tended to make connections between the different subjects we had to study," said alumnus Laurie Price.

The comfortable auditorium in the Arts Building filled gradually with the murmur of voices shortly before the convocation act. In the hallway, members of the school's chamber chorus, who have performed in Europe, were singing for the fun of it. "It's by Praetorius, who I believe was a 16th century German composer," said one singer, a member of the graduating class.

The emphasis at Sidwell has always been on liberal arts, and Gray made a ringing defense of it in her convocation speech. "Liberality is what enables us to see our activity in a wider context," Gray said. "We have learned to think not only of political and personal freedom but of freedom as a state of informed cultural awareness and sensibility, of freedom as critical judgment and critical moral awareness."

Gray, who as provost at Yale University in 1974 became the institution's first highly ranked woman administrator and became the first woman president of the University of Chicago in 1978, called on Sidwell to continue its liberal tradition.

The teaching and learning engaged in by Sidwell students was evident everywhere yesterday. The convocation song performed by the chamber chorus was an ambitious rendition of Walt Whitman's poem, "Three Leaves," set to music by '81 alumnus James Randolph Hostetler.

The complex poem was received with thunderous applause.