In January 2012, an unpublished study of the University of Pennsylvania, involving a randomized experiment, considered the experiment with the highest level of scientific evidence. The data comes from schools in South Korea, where a law was passed randomly assigning students to schools in their district. The study by Park, Berhman and Choi titled "Causal Effects of Single-Sex Schools on College Entrance Exams and College Attendance: Random Assignment in Seoul High Schools" concluded that "Attending all-boys schools or all-girls schools rather than attending coeducational schools is significantly associated with higher average scores."