LAS VEGAS — Four Las Vegas teenagers pleaded guilty Tuesday to voluntary manslaughter in the fatal beating of their high school classmate, as part of a deal with prosecutors that kept them from being tried as adults.

The teens originally were charged in January as adults with second-degree murder and conspiracy in connection with the November death of 17-year-old Jonathan Lewis Jr. The attack was captured on cellphone video and shared widely across social media.

Each teen faces…