The Post has ranked the best high schools in the Washington area and nationwide using a system called the Challenge Index. Designed by Class Struggle columnist Jay Mathews, the Index ranks schools by the number of Advanced Placement, International Baccalaureate or other college-level tests it gave in 2010 divided by the number of graduating seniors. The results from Mathews’ formula show how well each school prepares students for college. Find out where your child’s school ranks, and read Mathews’s story on the different ways two seemingly similar high schools challenge their students with college-level courses.