What makes a great teacher great? That's the question at the heart of 50 Great Teachers, from the NPR Ed Team.
Sarah Hagan has a passion for math, and the pi-shaped pendant to prove it.
The 25-year-old teaches at Drumright High School in Drumright, Okla. The faded oil town is easy to miss. Fewer than 3,000 people live there, and the highway humps right around it.