text: The Washington Post’s Jay Mathews uses a simple metric to measure challenging high schools. He divides the number of Advanced Placement, International Baccalaureate and Advanced International Certificate of Education tests a high school administers, by its number of graduates.
  
  Coeur d’Alene Charter Academy
  
  Schools made the list by scoring at least a 1.0 — that is, at least one advanced test per graduate. Riverstone International, a private school in Boise, scored a 5.889, tops in the state.
  
  Meanwhile, two Idaho high schools fell off the list for 2016: Renaissance High School in Meridian and Wood River in Hailey.
  
  For this year’s list, Mathews also looked at the poverty rates for schools that made the cut — looking at the percentage of students who were eligible for free or reduced-price lunch. Only one Idaho school had a poverty rate above Idaho’s statewide average is 49 percent; Vallivue had a 63 percent poverty rate.