By BENJAMIN SOSLAND

In a 1994 Financial Times article, critic Alistair Macauley asserted that Barbara Cook "is the only popular singer active today who should be taken seriously by lovers of classical music." By any measure, Ms. Cook's achievements are considerable. She created touchstone roles on Broadway such as Marian the Librarian in The Music Man and Cunegonde in Candide; she has been awarded Tony, Grammy, and Drama Desk awards; she has even been named a Living New York Landmark. Ms. Cook's career, already stretching over five decades, shows little sign of abating. In January, at the age of 78, she was presented at the Metropolitan Opera in a solo show, making her the first female pop-cabaret singer to give a solo concert at the Met in its history.

Barbara Cook (left) coaxed a more intimate performance from soprano Erin Morley (right), as she sang directly to Alex Mansoori, with Michael Baitzer accompanying. (Photos by Peter Schaaf)

So it was with some anticipation that more than 600 people, many of them presumably avowed lovers of classical music, made their way to the Peter Jay Sharp Theater on December 1 for a master class featuring Ms. Cook and students from the Vocal Arts Department. In his introductory remarks, President Joseph W. Polisi called Ms. Cook "sunshine incarnate," praising both her artistry and her deep humanity. He also jokingly admitted to an exchange he had with Ms. Cook before he took the stage to introduce her: neither he nor she could recall exactly how many classes she had given at Juilliard over the years, but both seemed pleased that it was more than they could remember.

Ms. Cook began the class with comments directed toward young performers. "When we are just starting out, we feel we are not enough," she said, adding that she tried all sorts of "crazy things" when she was young, especially in her efforts to get noticed at auditions. Over the years, she has come to realize that when performers have the courage to accept and share their gifts on an intimate level, they create a sense of "deep communication you can't put words to."

Then the work began. Alex Mansoori, a fourth-year undergraduate studying with Stephen Smith, was the first student of the afternoon. Together with graduate collaborative pianist Paul Kwak, Mr. Mansoori gave a tender performance of Stephen Flaherty and Lynn Ahrens's "The Cuddles Mary Gave" from A Man of No Importance. After hearing the song straight through, Ms. Cook claimed she was "put off" by Mr. Mansoori's "stilted speech." She wanted him to sing in a way that was "as close to talk as you can get."

In this assessment, she established what turned out to be the unvaried theme of her class. But to students of classical repertoire, who learn to sing without the aid of amplification, and for whom a specific kind of diction is a key component of their training, such a request is much more difficult than it may sound. (Moreover, musical theater repertoire, from which the afternoon's vocal selections were drawn, is also unfamiliar territory for Juilliard's singers.) In essence, Ms. Cook asked the six technically savvy singers who performed that afternoon to eschew an important part of their training, to take a more vernacular approach to diction, and to do so in front of an audience of hundreds. As the afternoon progressed, Ms. Cook tried various ways to shape the students' performances to conform to her notion of naturalness, with decidedly mixed results.

When soprano Erin Morley, a member of the Juilliard Opera Center and student of Edith Bers, together with pianist Michael Baitzer, sang Stephen Schwartz's "With You" from Pippin, Ms. Cook, who did not seem to know the song, acknowledged Ms. Morley's "beautiful voice." But of the actual performance she said, "I don't hear you letting us in." "Think of lyric as dialogue," she added. She then had Ms. Morley sing the song directly to Mr. Mansoori, who gamely went back up on stage.

Of the afternoon's six singers, Ms. Cook seemed most impressed with soprano Jennifer Sheehan. A third-year undergraduate studying with Stephen Smith, Ms. Sheehan sang a convincing rendition of Sondheim's "Not a Day Goes By" from Merrily We Roll Along with the sort of non-classical diction that clearly appealed to Ms. Cook. She praised Ms. Sheehan, saying, "I think you're really on the right track."

The theme of the class continued unabated with Michael Kelly, a graduate tenor studying with Marlena Malas. Mr. Kelly sang only a few phrases of "Low and Lazy" from The Sweet Bye and Bye by Vernon Duke and Ogden Nash when Ms. Cook interrupted him: "I don't want you to perform, I want you to talk to us." For Ms. Cook's taste, Mr. Kelly's voice was clearly too operatic. She wanted him to "avoid formality" and to "get off the page." "Worry about the notes when you're learning the song," she said. Wondering aloud how she might get him to loosen up, a member of the audience shouted out, "Tell him to take off his tie and jacket!" Ms. Cook laughed and said, "Why didn't I think of that?" After Mr. Kelly removed his jacket and tie, she asked him to have a seat on stage, and to loosen his faithfulness to the score's notation in favor of a more conversational approach.

The most poignant moment in the afternoon came when soprano Ariana Wyatt, a member of the Juilliard Opera Center also studying with Ms. Malas, took the stage. Although she did not appear to be familiar with the song, Ms. Cook wanted to know "why on earth" Ms. Wyatt chose Gershwin's "In the Mandarin's Orchid Garden" from Ming Toy. Ms. Cook asserted that the song did not suit the format of the class because it lacked emotional depth. (Prior to the class, she had asked students to choose music that had deep emotional meaning for them.) Ms. Wyatt's response was courageously candid: To her, the song was about feeling "out of place with a situation." She admitted to feeling a strong connection to it because "I feel out of place," having never sung musical theater before. After Ms. Wyatt sang the first few notes of the song, Ms. Cook stopped her and requested that she "try to not to be concerned with sound." Ms. Cook's idea of a natural style of delivery proved difficult for a classically trained singer, for whom naturalness has other connotations, to achieve on the spot. Both teacher and student were clearly frustrated. Ms. Wyatt left the stage, momentarily overcome with emotion. She composed herself and returned to give a searing performance.

The final performer was bass Matt Boehler, a member of the Juilliard Opera Center and a student of Stephen Smith. After the first few bars of Edward Heyman and Victor Young's "When I Fall in Love" from One Minute to Zero, Ms. Cook once again stopped the performance. "We don't want to hear singers singing the way they 'ought' to sing," she said. She asked Mr. Boehler to recite the lyrics. "You don't even have to sing with that voice!" she said of his rich bass. Mr. Boehler dutifully scaled down his sizable instrument to offer an intimate performance that incited swoons from some quarters in the audience.

In the brief question-and-answer session that followed, Ms. Cook credited Mabel Mercer and Judy Garland with shaping her basic notions about performing and song interpretation. Ms. Cook and her pianist Eric Stern closed the afternoon with a performance of "A Wonderful Guy" from South Pacific.

Benjamin Sosland, a D.M.A. candidate in voice, also serves as publications coordinator and assistant to the administrative director in the Vocal Arts Department.