City officials said the achievement gap for students of color in New York City public schools still needs to be addressed.
Newly released state test scores for English and math showed a slight improvement citywide since last year.
The State Department of Education reported 35.2 percent of the city's about 1.2 million students met proficiency standards in math in 2015, compared to 34.2 percent in 2014.
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In English, 30.4 percent of New York City students scored proficiently, up from 28.4 percent last year.
One look at the demographic breakdown, however, and the gap between black and Latino students and their white and Asian peers persists.
Overall, both white and Asian students tested above 50 percent proficiency in English, while Latino and black students scored below 20 percent.
Asian students scored the highest in math with 66 percent, followed by white students with about 55 percent. Some 23 percent of Latino students also scored well in math, compared to less than 20 percent of black students.
De Blasio told reporters on Wednesday that the battle to close the gap is yet to start in earnest.
"We have not yet begun to fight," the mayor said. "We have just started. This is the real answer – we have just started. And that gap will be addressed."
De Blasio focused instead on the report's silver linings.
"We see progress here," the mayor said. "We see improvements for our English-language learners, improvements for the young people who finished their English-language learning experience and then went on. We see improvements for Latino students, improvements for African American students, but it’s not enough."
Critics of the de Blasio administration's education policy pounced on the modest success.
"When more than two-thirds of students aren't being taught to read and write on grade level, you have to question who this system is designed to serve," said Jenny Sedlis, executive director of pro-charter school and reform group StudentsFirstNY, in a statement. "Incremental gains are not going to cut it."