"I've taken a few practices," he said. "It was no surprise, but science was the hardest."
He said there was a section dealing with physics that completely baffled him. Although his score was just 3 points shy of perfect, Rosen said he wanted to do better.
"I had decided if I got a 34, I wouldn't retake it," Rosen said.
He set this original benchmark because he was eyeing a Brigham Young University scholarship, and he had come to the conclusion that scoring at least 34 would maximize his chances of getting it.
Rosen said he didn't do a whole lot different the second time he took the test except one key thing.
"I was on time," he said.
He said one thing that really helped him was advancing to a calculus class and learning higher concepts of math.
The news that he got a perfect score added to his holiday cheer as Rosen learned of his achievement around Christmas time.
"I was excited, but I was really surprised," he said.
Although he felt confident that he'd done well on the test, Rosen said he thought he might have met his goal and nothing more.
"I was expecting a 34," he said. "It was surreal for a little bit after."
The ACT consists of four sections: English, math, reading and science. Each category is scored on a scale of 1 to 36. The overall score is an average of the four sections.
According to the ACT website, on average, less than one-tenth of 1 percent of test takers earn a 36. In 2012, only 781 of more than 1.66 million graduating high-school students earned a perfect score.
Rosen still has the rest of this year and his senior year left before graduating, but he knows where he wants to go to college.
"I'm a BYU fan, although I wouldn't mind going to the [University of Utah] or Utah State," he said.
The ACT score is one of the admission criteria that colleges and universities consider, but Rosen said he hopes his high score will help him get scholarships as well.
He said he's undecided about what major to pursue in college, but his dad's profession as an orthopedic surgeon has inspired him to consider the medical field.
"My dad's a doctor, and since I was little, that's kind of what I wanted to do," he said.
His favorite classes are AP calculus and AP U.S. history, but he also devotes a lot of time to music and theater.
"I have been playing the cello since preschool and have been playing the piano for nine years," Rosen said. "I do musicals. I just think it's fun, and I enjoy doing stuff onstage."
Keith Wood is Rosen's AP U.S. history teacher this year. He also taught Rosen in an honors sophomore English class last year.
Wood said he's not surprised that Rosen got a 36 ACT score.
"He's an extremely hard worker, smart to begin with but a hard worker," Wood said. "He's concerned about the quality of his work."
Wood called Rosen a "remarkable student," and someone who is humble about his accomplishments and shows respect to others.
"He's approachable, and he's not arrogant, stuffy or pretentious," Wood said.
Murray High principal David Dunn has known Rosen since Rosen was in seventh grade.
"I've got nothing but positive things to say about him," Dunn said. "I think it's a great accomplishment. He's a junior; he's not even a senior."
Like Wood, Dunn praised Rosen's academic achievement and likable character.
"He's an outstanding young man," Dunn said. "He's very liked by his classmates, very polite and respectful, and a good example of [what] Murray High students academically strive to achieve."
Acing the test
The test consists of English, math, reading and science and an optional writing test.
On average, less than one-tenth of 1 percent of test takers score a perfect 36.
Only 781 of more than 1.66 million graduating high-school seniors earned a perfect score last year.