Efron was born in San Luis Obispo, California, and later moved to Arroyo Grande, California. His father, David Efron, is an engineer at a power plant, and his mother, Starla Baskett, is a former secretary who worked at the same power plant. Zac Efron has a younger brother, Dylan, and had a self-described "normal childhood" in a middle class family. He is an agnostic, having never been religious. His surname, "Efron", means "lark" in Hebrew (his paternal grandfather was Jewish).
Zac Efron has said that he would "flip out" if he got a "B" and not an "A" in school, and has also described himself as having been a class clown. Zac Efron's father encouraged him to begin acting when Zac Efron was 11 years old. He subsequently appeared in theater productions at his high school, worked in a theater called The Great American Melodrama and Vaudeville, and began taking singing lessons. Zac Efron performed in plays such as Gypsy; Peter Pan; or, The Boy Who Wouldn't Grow Up; Little Shop of Horrors; and The Music Man. He was recommended to an agent in Los Angeles by his drama teacher, Robyn Metchik (the mother of actors Aaron Michael Metchik and Asher Metchik). Efron was later signed to the Creative Artists Agency.
Zac Efron graduated from Arroyo Grande High School in 2006, and was then accepted into the University of Southern California, but has deferred his enrollment to work on film projects. Zac Efron also attended Pacific Conservatory of the Performing Arts, a community college located in Santa Maria, California, which provided him with the opportunity to perform as a "young player" during the years of 2000 and 2001.