She was jet-lagged from her press tour and going on only four hours of sleep. But in an eight-minute phone interview, Toni Collette still focused on one thing: challenges.

“I look to be challenged,” she said, in the upbeat Australian accent that is rarely heard in her diverse performances. “I just don’t ever want to be bored or complacent.”

It’s probably safe to say that boredom and complacency haven’t plagued the 40-year-old Collette, whose newest film, “The Way, Way Back,” opens here Friday (see review at left). Collette, who grew up in the suburbs of Sydney, Australia, and made her first on-screen appearance in 1990, earned an Oscar nomination in 2000 for her supporting role in “The Sixth Sense.” By the end of the decade, she picked up an Emmy and a Golden Globe for her title role in the Showtime series “The United States of Tara,” in which she played a suburban housewife with dissociative identity disorder who takes on alternate personalities.

Since that show ended in 2011, Collette only dug deeper in new roles, entering the most prolific period of her career so far. Her recent roles include a rebellious nanny in the Australian comedy “Mental” and Alfred Hitchcock’s assistant in the biopic “Hitchcock.” She’s working on nearly 10 projects for the next two years.

Many actors who hit it big on TV find it impossible to move on from their signature character. Collette realizes she was lucky to avoid that with “Tara,” because her role was actually several characters in every episode.

“It was such a pinnacle for me, and I was so spoiled to be able to play so many varied characters,” she said. “I just need to look for opportunities where I can be just as creative, where I can feel just as challenged and just as satisfied.”

In “The Way, Way Back,” which stars an ensemble of comic actors, Collette plays Pam, the mother of Duncan, a moody 14-year-old who hides his hatred for his mom’s cruel boyfriend, Trent (Steve Carell), while the family vacations. Duncan eventually finds solace in the lovable losers at Water Wizz, a local amusement park.

On the surface, “The Way, Way Back” seems like the familiar territory Collette wants to avoid: She previously co-starred with Carell in “Little Miss Sunshine,” also playing the mother in an indie-perfect dysfunctional family.

The promotional materials for “The Way, Way Back” eagerly note that it is from the same studio, Fox Searchlight Pictures, that distributed “Sunshine.” But Collette said she doesn’t “think the characters are similar at all,” and, in fact, found Pam a “frustrating” character.

“She’s so passive and inactive and has this idea about what she thinks is right for her and it has nothing to do with reality. She’s basically lying to herself about this relationship,” she said.

Ultimately, though, she was won over by the script’s focus on Duncan, and how this initially timid character becomes the catalyst for change that the other, older characters need.

“One of the things that I loved about it was the fact that, in today’s world, we just kind of assume that adults are all-knowing and kids need to be taught. But kids are so perceptive in handling things in their life,” she said. “I think the story ultimately is about a boy and his mom, and how someone else gets in the way for a minute, and then they reunite.”

More broadly, the film also appealed to one of the few running themes Collette looks for in her multifarious roles.

“I love stories that are about change and people struggling with change and yearning for change and not knowing how to implement it in their lives,” she said. It’s a problem that Collette, it seems, needn’t worry about in her own career.