Before the summer began, Regan Smith expected to devote much of July to a typical teenage rite of passage: taking driver’s ed classes. The month hadn’t even started when the brakes were put on that plan.

The 15-year-old from Lakeville saw her swimming career accelerate rapidly in June, as she made the U.S. team for the world championships in Budapest, Hungary. While her friends are learning three-point turns in a parking lot, she is making her first trip to Europe to compete alongside teammates such as Katie Ledecky and Lilly King.

Though Smith is the youngest swimmer since 2007 to represent the U.S. at the world championships, a whirlwind year left her more nervous about learning to drive than she is about racing Olympians in the 200-meter backstroke.

Thirteen months ago, Smith competed at the Olympic trials and felt every bit the rookie that she was. Since then, she has raced at her first international World Cup meets and grown from one of the country’s top age-group swimmers into an emerging star.

Smith entered last month’s U.S. championships simply hoping to make the team for the world junior championships. Surprised as she was by her performance in the 200 back — where she finished second to Olympic silver medalist Kathleen Baker — the giant steps she’s taken in the past year groomed her for the biggest one yet. She’ll swim Friday at the world meet, which begins Sunday.

“I didn’t think I’d be able to do it. I really didn’t,” said Smith, who is ranked eighth in the world after clocking a time of 2 minutes, 8.55 seconds in the finals at nationals. “I’m really happy, because I feel like I earned it.

“Over the past year, I’ve gained so much experience, so much seasoning. Compared to last year [at the Olympic trials], I felt like I belonged. I felt like I knew what I was doing. I feel like all my hard work has been rewarded, and I’m really excited.”

Smith’s breakthrough wasn’t a shock to those who have been following her progress. Rowdy Gaines, a three-time Olympic gold medalist who is NBC’s swimming analyst, started tracking Smith about 18 months ago after a USA Swimming official told him she was a prodigy.

Gaines called her swims at nationals “spectacular,” and he already is comparing Smith to Krisztina Egerszegi — considered by many the greatest female backstroke swimmer in history.

“She has an incredible feel for the water,” Gaines said. “She’s so relaxed, and she has a mix of endurance and speed. I’m really impressed with what she did [at nationals]. It was really special, especially at age 15.”

A sophomore-to-be at Lakeville North High School, Smith made an instant splash in a sport she took up to stave off boredom and be with her sister, Brenna. She began competing at age 7½. By age 10, she was setting national age-group records; at 12, as a seventh-grader, she finished second in the 100-yard back and 100 butterfly at the Class 2A state championships.

That was Smith’s only season of high school swimming. She now trains with Apple Valley’s Riptide Swim Team, where she is coached by Mike Parratto, who molded Jenny Thompson into a 12-time Olympic medalist.

Smith dipped her toes into elite-level competition as a 13-year-old, when she finished fifth in the 200 back at an Arena Pro Series meet at the University of Minnesota. Seven months later, the Olympic trials provided another measuring stick. One of the youngest swimmers at the meet, Smith made the semifinals of the 100 backstroke and finished 13th, earning her invitations to World Cup meets in Tokyo and Hong Kong last fall.

She continued to flourish as she made her first trip overseas and her international debut with Team USA. By the end of the year, Smith had transformed from a wide-eyed newbie into a comfortable, composed athlete ready to claim her place.

“A year ago, it was a jaw-dropping thing for her to be competing against swimmers like this,” Parratto said. “She’s a talented girl, but this is a whole different level.

“She’s learned so much from these experiences. In Tokyo and Hong Kong, she was competing in finals with Olympic medalists. And now, at 15, she’s world-ranked. She knows she belongs.”

Gaines said Smith has all the ingredients for a stellar career: a long, lean build, impeccable technique and a coach who is not rushing her development. A committed athlete who never misses a practice, Smith trains and competes at all distances and strokes.

Her experience in high-stakes meets paid off at last month’s national championships in Indianapolis. After clocking the second-fastest time in the preliminaries of the 200 back, she recognized she had a shot at making the roster for the world championships, but she told herself it was OK if she didn’t.

Smith wound up with a place on the team, a personal-best time and a sudden shift in her summer schedule. After Hungary, she will race at the world junior championships in Indianapolis in late August.

She’s also hoping to squeeze in the rest of those driver’s ed classes before summer ends. But with her swimming career moving full speed ahead, she’s willing to wait a little longer for her learner’s permit.

“I want to go into the world championships with an open mind and try to gain as much as I possibly can from the experience,” Smith said. “It’s pretty cool that I’m a high school student, and I get to do something like this. I feel really thankful.’’