Pat Wolf has an article summarizing and clarifying the latest evidence from the official evaluation of the D.C. voucher program newly posted at Education Next.
The part that struck me the most was how strong the DC voucher results are compared to the results of all of the other rigorous evaluations sponsored by the U.S. Department of Education:
The achievement results from the D.C. voucher evaluation are also striking when compared to the results from other experimental evaluations of education policies. The National Center for Education Evaluation and Regional Assistance (NCEE) at the IES has sponsored and overseen 11 studies that are RCTs, including the OSP evaluation. Only 3 of the 11 education interventions tested, when subjected to such a rigorous evaluation, have demonstrated statistically significant achievement impacts overall in either reading or math. The reading impact of the D.C. voucher program is the largest achievement impact yet reported in an RCT evaluation overseen by the NCEE. A second program was found to increase reading outcomes by about 40 percent less than the reading gain from the DC OSP. The third intervention was reported to have boosted math achievement by less than half the amount of the reading gain from the D.C. voucher program. Of the remaining eight NCEE-sponsored RCTs, six of them found no statistically significant achievement impacts overall and the other two showed a mix of no impacts and actual achievement losses from their programs.
Jay P. Greene's Blog 
BOOOOOOOOOOOOOOOOOOOOOOOOOOM!