Civil rights activist Sylvia Mendez, a winner of the Presidential Medal of Freedom, spoke this week at the Museum of African American History’s Martin Luther King Jr. celebration, sponsored by Suffolk University. When she was 8, Mendez and her brothers were blocked from attending school in Westminster, Calif., because of the color of their skin and because they’re Mexican. (Their mother was Puerto Rican.) Along with other families, they filed a lawsuit to end the discriminatory policies — and won. Their victory desegregated schools for Latinos seven years before the Supreme Court desegregated schools nationwide in Brown v. Board of Education. Now 80, Mendez travels the nation to spread the word about this overlooked part of history and the work left to be done.