Doing it once is considered to be a feat. Doing it twice is the start of a streak. Doing it a third time? That means it's becoming a habit.

"This is our third time in a row and it's absolutely thrilling," Iswari Natarajan, said.

She teaches Advanced Placement calculus at St. Mary's Academy in Englewood, an all-girls private school. For the third year in a row, all of her students who took the AP Calculus Exam for college credit obtained the highest score of five.

"We go in as a group of, it's an all-girls high school and my objective is I am building confidence," Natarajan said. "We are showing them if you can do this, you can do anything."

This year, 21 students scored a five on the AP Calculus AB and AP Calculus BC exams offered by College Board. Natarajan says the key is teaching her students how to be successful in life -- not just in calculus.

"I think teaching beyond the subject is important," Natarajan said. "So, it's never about content for me. I always talk about attitude and talk about grit. I talk about embracing failure."