Then they learned the real reason they'd been gathered there: a private foundation underwritten by the convicted former junk bond financier Michael Milken was about to hand a check for $25,000 (Pounds 15,600) to one of their teachers. Adding to the sense of suspense was the fact that no one - not even the recipient - knew who would get the money.
It was the first of $3.5 million the Milken Family Foundation has handed out to 150 US teachers this autumn, no strings attached, for their "exceptional educational talent".
But the purpose of the surprise gift also was to persuade audiences of students that a career in teaching pays rewards at a time when a severe teacher shortage is anticipated. The US department of education estimates there is a need for two million more teachers in the next 10 years because of a continuing increase in school enrolment.
"We are quick to recognise greatness in so many other professions. We do it in sports. We do it in music," said Mr Milken's son, Lowell, the foundation's president. "It's not often that someone walks into a school and recognises greatness in educators."
Michael Milken, who pleaded guilty to six counts of securities fraud in 1990 in connection with an insider-trading scandal, served two years in prison, paid more than $1 billion in fines and was banished from the securities business for life. But he has invested much of his remaining fortune in education and health causes.
The immediate impact of his cash gift in the Boston auditorium was undeniable.
There were gasps and whistles when students and their teachers learned they had been gathered on a pretence and were really there to watch a check for $25,000 go to someone in the room. There was a standing ovation when the winner's name was read: Michael Contompasis, the 58-year-old headteacher, who slapped his hands to his head.
But, as they filed out, few students said they'd changed their minds and would now pursue a career in education. "It's nice to honour people that want to be teachers, but I don't want to be one," said Marybeth Foley, 17. "I don't want to work with kids because I see how kids treat teachers."
Keara Whitsey, 17, said she didn't plan to be a teacher, either. "I don't have the patience," she said.
Mr Milken's gesture may be laudable, said Kathleen Lyons, spokeswoman for the National Education Association, the nation's largest teachers' union. But, she added, "The promise of $25,000 for 150 of them each year isn't going to make people say, 'Oh, boy, that's what I'm going to do to get that money'."
Ms Lyons and others said the awards distract attention from the larger issue, which they said was that teachers are being underpaid. Winners of the awards are chosen by each state's department of education for innovative teaching methods, ability to instil character and self-confidence in students and commitment to professional development.
The money can be spent on anything, though some recipients give it to their schools. But others have purchased cars or taken holidays.