SAN JOSE -- Economics teacher Sam Lepler had the most students in the entire world earning perfect scores on the advanced placement exams this year. And yet The Harker School teacher is modest and a bit bewildered.

It could be in part that he received no official notice of his accomplishment. Or that he's insistent that his students receive credit. Or that he was busy Friday grading finals. But his students give him much of the credit.

Last month Harker, the elite private academic powerhouse, learned it was the only school in the world with 10 students earning perfect scores on last spring's AP exams. All of them earned their perfect scores on the AP microeconomics exam. One of those students, Ashvin Swaminathan -- now a freshman at Harvard -- correctly answered every question on the macroeconomics exam as well, bringing Harker's perfect-score total to 11.

How rare is this? Out of 67,782 students taking the microeconomics AP test in May, only 33 answered every question correctly. And Swaminathan was one of only 12 students worldwide to do that in macroeconomics, and one of four in the world to earn a perfect score on two AP exams.

The College Board, which administers AP tests, called it "an extraordinary academic achievement." In October it sent letters to each perfect-scoring student -- but not to the teacher nor, initially, to the school.

Senior Angela Ma, one of the Harker 10, took a screen shot of her letter, emailed it to Lepler and expressed her gratitude. Other students hearing about perfect scores did the same.

"When I found out we had even one," Lepler said, "I said, 'Wow, that's amazing.'"

Then he heard about a second, and third and more. So Harker inquired with the College Board, and in November received a letter saying Harker had 11 perfect-score AP tests.

Lepler didn't see the letter until a reporter forwarded it to him Friday.

Connect material

The exams assess what students have learned in high school advanced-placement classes, which cover college-course material. Students take the proctored exams in May and are scored on a 1-to-5 scale. A 5 is equivalent to an A or A-plus. The University of California awards college credit for scores of 3, 4 or 5; credit policies vary in private universities. Lepler found out in July that 87 percent of his six dozen students earned 5's, with nearly all the rest earning 4's.

"I feel really proud of what my students were able to accomplish," said Lepler, 31, in his seventh year of teaching, four of them at Harker.

He denies having any secret, except to make his lessons applicable to real life. "If the kids don't connect the material to their daily lives, they don't get really interested."

In the yearlong elective, half macroeconomics and half microeconomics, he uses concrete examples. For a lesson on demand elasticity, for example, he asks students if the price of McDonald's burgers doubles, would you eat there less often? Yes, they answer. But even if the price of a cancer-fighting drug doubled, you'd still buy as much as you can afford. To explore the difference, he said, "We get into how to calculate price sensitivity."

He'll throw in a joke, or, in teaching the challenging subject of money creation, he'll tell a wild yarn about a mythical miner ancestor living in the wild West who stashes away his gold and creates a banking system.

His passion and enthusiasm for economics are contagious. "Mr. Lepler is a really fun teacher and makes us all fall in love with the subject," said senior Rahul Sridhar. "By the end of the year your whole world view is changed, because you see the world through an economist's eyes."

Engagement and motivation are key for students. "Because they really do want to understand a subject," Jennifer Gargano, assistant head of school, said, "this might contribute to high accuracy."

"So exciting"

Sridhar and other perfect scorers participated in the National Economics Challenge, a competition that covers material from upper-division college course. In 2012, the four-member Harker team came in second in the nation; last year, the school placed third in California, just one question behind the winning team.

Exposure and understanding of advanced material helps prepare students for the AP exam. "When you have a really deep understanding, the AP level is easy," Lepler said. "I love it. It is just so exciting. They challenge me, I challenge them."

He reviews with students how they do on weekly quizzes, and on tests and practices. Having an average class size of 15 -- compared with more than 30 in public high schools -- helps, he said, so he can offer more individual attention.

At Harker, where the annual high school tuition is $38,900, admissions are selective. "Having the students we have makes any teacher look good," he said.

His students disagree. "He made it feel like so fun and so worth it to work hard," Ma said.

When he learned about the perfect scores, "he kept saying, 'This is not me, this is you guys,'" she said.

"But we know 11 is not a coincidence. He is definitely responsible."

Contact Sharon Noguchi at 408-271-3775. Follow her at Twitter.com/NoguchiOnK12.

AP scores by the numbers
Number of AP exams taken in 2013: about 4 million
Number of students taking AP exams: about 2.2 million
Number of students worldwide earning a perfect score: 109
Number of students taking AP microeconomics exam: 67,782
Number of perfect scores in AP microeconomics: 33
Number of Harker students with perfect scores in AP microeconomics: 10
Number of students worldwide earning a perfect score in AP macroeconomics: 4
Number of Harker students with a perfect score in AP macroeconomics: 1

Harker's perfect scorers
On AP microeconomics: Jennifer Dai, Aaron Huang, Savi Joshi, Vikram Naidu, Anisha Padwekar, Kevin Duraíswamv, Brandon Yang, Angela Ma, Rahul Sridhar and Ashvin Swaminathan
On AP macroeconomics: Ashvin Swaminathan