The 20 colleges with the largest populations of D.C. Tuition Assistance grant (DCTAG) recipients have a combined graduation rate of 39 percent for those students, according to program data, the Washington Post reports. Is that a good statistic, or a bad one? On the one hand, it’s low. On the other hand, the data come from a college-preparatory operation that has dramatically increased the share of students from D.C. public schools who enroll in college at all. DCTAG officials have taken to posting the grad rates in high schools, so students will “give more thought to school selection,” said Gregory J. Meeropol, deputy assistant superintendent in the Office of the State Superintendent of Education…