They used to sing together in choir ensembles at New Trier High School, but now Will Hart and Danny Rubenstein are musical competitors.

And the entire country gets to watch, on prime time television. The former New Trier classmates found themselves and their college a cappella groups as opponents on the NBC talent show contest “The Sing-Off,” which starts a new season Sept. 19.

The two were a year apart in high school, and knew each other well. They were both in New Trier’s prestigious Swing Choir group. They even fit the same general description: tall, with red hair. ...

Hart grew up in Kenilworth and started singing with his family’s church choir at the Kenilworth Union Church.

His father went to Dartmouth to study engineering, just like him.