NEW YORK (TIP): Richard Carranza, who oversees the nation’s largest schools system, will step down after about three years as chancellor. He will resign in March. The abrupt move comes after disagreements between Mayor Bill de Blasio and Mr. Carranza over school desegregation policy reached a breaking point in recent weeks. Mr. Carranza, 54, is leaving one of the most influential education jobs in America about three years after he was appointed, and just 10 months before the end of Mr. de Blasio’s second and final term. He will be replaced by Meisha Porter, a longtime city educator and current Bronx superintendent who will become the first Black woman to lead the sprawling system, which has over 1 million students and 1,800 schools. Ms. Porter, 47, will take over as chancellor on March 15.