Majority Black schools are generally made up of a poorer student body, and unfortunately poorer students usually mean less parental involvement, with no private academic or test tutors to make up for it.
The problem may be more significant than less parental involvement. Some poor kids are showing up to kindergarten with cognitive delays. Their parents don't have conversations with them, only give orders so the kids have limited vocabularies. Parents feed the kids low nutrient convenience foods. The kids haven't been taught how to cooperate/play with other children.
Schools exacerbate the problem by heavily focusing on academic rigor which is usually developmentally inappropriate for even children with the best of parents. In order to increase test scores, recess and the arts are usually the first to go. Over the last 10 years SAT scores have dropped for all ethnic groups except for Asians, whose scores have risen.
Off-topic: Filipinos used to underperform whites but in the last 20 years the achievement gap has been closed, completely. You don't hear a word about it. Not a word.
Lower threshold for sports and weak extracurricular, majority-White schools tend to have a higher GPA threshold for sports (where many majority Black schools excel) leading student athletes to have to reach higher to play sports, the consequence being they also have better grades when applying for college.
GPA requirements for athletes is usually determined by the school district or even the state. Where have you seen majority white schools being held to a higher standard?
If what you are saying is true, then if blacks were held to a higher standard activists would be screaming about discrimination and a school to prison pipeline. Education activist never want black children held to the same standards as whites.
One school district diversified their gifted program by lowering the test standards for low-income and English language learners which allowed them to legally kick white kids out of the program.
How Can Schools Address Inequality in Their Gifted-and-Talented Programs?
The NAACP filed a complaint against New York City Department of Education because too few blacks and Hispanics were getting into the specialized exam schools like Stuyvesant and Bronx Science. Instead of the NAACP setting up a program that would get black students to do well on the admissions test, the NAACP wanted the admissions standards changed to include factors like geography.
LDF, LatinoJustice PRLDEF and The Center for Law and Social Justice at Medgar Evers College File Complaint Challenging Admissions Process at NYC Public Specialized High Schools | NAACP LDF
Go figure... 
