WATCH: 'Hamilton' cast member sings with CAPA students

Sydney James Harcourt, who understudied Philly's Leslie Odom Jr. as Aaron Burr in the original cast of the Broadway smash "Hamilton," dropped by the choir rehearsal room at Philadelphia High School for the Creative and Performing Arts (CAPA) on Wednesday afternoon to sing with 22 lucky students.

"All right, Philly!" he yelled after their first pass through the music. Then the students got down to brass tacks, sight-reading four songs from Lin-Manuel Miranda's Tony-winning musical: "Wait for It," "The Room Where it Happens," "History Has its Eyes on You," and "The Story of Tonight."

The CAPA students and Harcourt had come together to rehearse for an April 8  performance at an opening gala for the new Museum of the American Revolution at 3rd and Chestnut Street. Harcourt will also perform at the Museum's grand opening ceremony on April 19.

He'll be in good company: The museum announced Wednesday that celebrity speakers on opening day will include former Vice President Joe Biden, author David McCullough, and journalist Cokie Roberts.

At CAPA, Harcourt's instructions to the 10th, 11th, and 12th graders were clear and their attention to him rapt as they sang together from arrangements the students had only just seen for the first time. "A lot of people on Broadway can't do what you're doing," he said. "They can't come into a room and read this quick."

He encouraged them to always "make it about your best work," because on Broadway there's very little room for an off-day.

Before rehearsal, senior vocal major Marissa Garcia admitted to feeling nervous. "Musical theater is my livelihood," she said. "I'll take the nerves and put it towards my music."

Their teacher, Dorina Morrow, said their exposure to the demands of sight-reading and their brush with celebrity were priceless experience for the young singers. "I'm hoping his magic will rub off on them."