The Senior Jazz Band of Newent Community School provided the music at the Wyastone concert hall near Monmouth last weekend.
The 25 youngsters were the warm-up act at a £30-a-head dinner.
Head of Music Mary Wrenn said: "I was proud of them, and the acoustics were incredible."
The band played a number of swing classics, including a spirited rendition of New York, New York.
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