Perennial winner Julia R. Masterman Laboratory and Demonstration School in Philadelphia again ranked first.
Nationwide, Radnor is the 525th best high school, U.S. News said.
Conestoga High School was the only local high school to beat out Radnor. Conestoga was ranked at No. 5.
Nearby, Great Valley High School was No. 10, Lower Merion High School was No. 15 and Harriton High School, also in the Lower Merion district, was No. 25.
Each year, U.S. News joins forces with the American Institutes for Research to evaluate schools on overall student performance on state-mandated assessments, as well as how effectively schools educated their black, Hispanic and economically disadvantaged students.
Performance on Advanced Placement and International Baccalaureate exams is used to determine the degree to which schools prepare students for college-level work.
Schools were ranked within each state, as well as on a national stage.