Not the black boys who persist through the charters schools, but those who leave.
All the study author is really saying is that black boys have a higher dropout rate, which is not surprising. I still maintain that the elite charters, KIPP, Uncommon Schools, Achievement First, etc., offer the best academic opportunities for urban black boys.
From the Education Week story about the study:
KIPP charter middle schools enroll a significantly higher proportion of African-American students than the local school districts they draw from, but 40 percent of the black males they enroll leave between grades 6 and 8, says a new nationwide study by researchers at Western Michigan University. "The dropout rate for African-American males is really shocking," said Gary J. Miron, a professor of evaluation, measurement, and research at Western Michigan University, in Kalamazoo, and the lead researcher for the study. "KIPP is doing a great job of educating students who persist, but not all who come."