Corrected entry: In the last dance scene, you clearly see Billy put on a record (I've had the time of my Life) for the dance. Later, while the same song is still playing they show band members playing the music. Did they join in mid-song?
LorgSkyegon
27th Aug 2001
Dirty Dancing (1987)
Correction: Mr. Kellerman says something like, "You have sheet music for this stuff?"
Kellerman asks the band director if he has sheet music because he sees the guests are really enjoying it. When he asks, the band is already playing along because you can see the cello player playing in the background. They likely joined in after they saw the crowd's reaction, but before Kellerman asks if he has sheet music. Being that the song was on record, it had obviously been out for a while, played on the radio, etc. so they likely had heard it.
Correction: The band is improvising along with the music, something a well-trained musician (especially with a jazz background) would be able to do.
LorgSkyegon