MIAMI — One of the country’s most prestigious education prizes was awarded Tuesday to the Miami-Dade County public schools for improving student achievement, raising the graduation rates of minority students, and increasing the percentage of minorities reaching advanced levels on state exams.

Miami-Dade, the country’s fourth-largest school district, had been a finalist for the Broad Prize for Urban Education five times before winning the honor this year. National education officials announced the award in New York.