In the face of growing pressure to tackle New York City’s widespread school segregation, Mayor Bill de Blasio announced on Saturday a proposal that would change how students are admitted to eight of the city’s specialized high schools, a group of highly sought-after institutions where students gain entry based on a single test.

Black and Hispanic students, who make up 67 percent of the public school population, are grossly underrepresented at the specialized high schools, which include Stuyvesant High School and the Bronx High School of Science.

Mr. de Blasio campaigned on the issue when he first ran for mayor in 2013, saying the specialized schools should “reflect the city better,” but he has yet to make a dent in the problem. This year, black and Latino students received just 10 percent of the offered seats at specialized high schools, a percentage that has held essentially flat for years.

“The Specialized High School Admissions Test isn’t just flawed — it’s a roadblock to justice, progress and academic excellence,” Mr. de Blasio wrote in an op-ed published Saturday on the education website Chalkbeat.