At the St. James School in North Philadelphia, educator Atiyah Harmon gathers about 25 students — all girls — in a circle to recite a creed: “I am my sister’s keeper, I love myself, I love to learn, I love to grow, I’m a beautiful Black girl … and I love math.” The students are members of Harmon’s after-school program Black Girls Love Math, or BGLM, a local nonprofit aiming to improve Black girls’ performance in the subject.