When They See Us: How did Korey Wise and Yusef Salaam know each other before?

WHEN THEY SEE US on Netflix dramatises the story of the Central Park 5. In 1989, 5 teenagers were wrongfully accused and later convicted of a crime they did not commit. Korey Wise and Yusef Salaam were 2 of the boys wrongfully convicted but how did they know each other before April 1989?