Since having her breakout moment four years ago, Jessica Chastain has established herself as Hollywood’s ideal of smart beauty. The Oscar-nominated star of The Help and Zero Dark Thirty, now onscreen as the ’80s-glam, viperish wife of a heating-oil businessman (Oscar Isaac) in A Most Violent Year, is renowned as a workhorse (she appeared in six movies in 2011 and four in 2014). But as the actress reveals, that wasn’t always the case.

“Nobody knows this about me,” says Chastain, 37, in a feature in this week’s EW. “I dropped out of high school. I was not a hard worker. I was a terrible student. Eventually I got my adult diploma, but I did not graduate. And it wasn’t that I just dropped out and never went back—at the end of the year I had too many absences to graduate.”

Chastain was an eccentric truant. “I would cut school and sit in my car, reading Shakespeare,” she says. Appearances in Bay Area productions of a number of the Bard’s plays, including the lead in a 1998 staging of Romeo and Juliet, led her to audition for the prestigious Juilliard School. And at age 22, she was accepted. “I got to Juilliard and I’d never been around literature like that,” she says. “It completely opened me up.”

But Chastain still thinks about the struggling young pupil she once was, and hopes her success could be an inspiration to underperforming kids in school now. “I thought that I wasn’t an intelligent person because I did so poorly,” she says. “There are kids out there that aren’t doing well in school—and I hope they never think it means they’re stupid. It’s all about finding where your interest lies and finding what you’re good at.”

For more on Chastain—including how a director wooed her into his next movie by tweeting her pictures of mongooses hugging each other—pick up this week’s issue of EW, on stands Friday.

A Most Violent Year
  • Movie
  • 125 minutes