An unheard recording of jazz legend Thelonious Monk performing at a high school in 1968 is set to be released by Impulse Records.

The surprise performance came about after 16-year-old student Danny Scher invited the iconic pianist and composer to perform at his high school in Palo Alto, Calif. Monk, who was then at the pinnacle of his musical career in a year of heightened racial tensions and political volatility, accepted the invitation. The concert took place Oct. 27, 1968, and the school’s custodian recorded it.

“That performance is the one of the best live recordings I’ve ever heard by Thelonious,” Monk’s son T.S. Monk, founder of the Thelonious Monk Institute, said in a statement. “I wasn’t even aware of my dad playing a high school gig, but he and the band were on it. When I first heard the tape, from the first measure, I knew my father was feeling really good.”

The 47-minute album features Monk’s steady touring band of tenor saxophonist Charlie Rouse, bassist Larry Gales, and drummer Ben Riley.

Included on the album is the lyrical love song Ruby, My Dear; a spirited, 13-minute ride of Well, You Needn’t; a solo piano reading of Don’t Blame Me by Jimmy McHugh; an “epic dance” through Blue Monk; and a playful take of Epistrophy.