To quote from the article:
"While teacher effectiveness may be the most salient in-school factor contributing to student academic outcomes, it contributes a relatively small slice — no more than 14 percent, according to a recent RAND Corporation analysis of teacher effectiveness — to the overall picture. A far bigger wedge is influenced by out-of-school variables over which teachers have little control: family educational background, the effects of poverty or segregation on children, exposure to stress from gun violence or abuse and how often students change schools, owing to homelessness or other upheavals."
"Teaching does matter, and it can improve. But there is little evidence — at least to date — that it can counter the effects on children of attending neighborhood schools that remain racially and economically isolated."
I find this attitude difficult to reconcile with other things I've read about teaching poor and minority kids. For example, here is a summary of a few studies as reported in Teaching as Leadership :
"The schools that are highly effective produce results that almost entirely overcome the effects of student background" 
"Having a top-quartile teacher rather than a bottom-quartile teacher four years in a row would be enough to close the black-white test score gap" 
"Differences in this magnitude -- 50 percentile points in just three years -- are stunning. For an individual child, it means the difference between a 'remedial' label and placement in the accelerated or even gifted track. And the difference between entry into a selective college and a lifetime of low-paying, menial work" 
Many charter schools use a lottery to determine which students are enrolled, and many studies have taken advantage of such 'natural experiments'. This paper  represents a good overview of such studies. It seems that some charter schools can have significant effects on learning. In a Boston study, "Abdulkadiroglu et al. (2011)...find very large average effects: charter school attendance increases state-level English/language arts and math performance test scores by 0.2 and 0.35 standard deviations per year respectively. Given that that the achievement gap between black and white students in Massachusetts is about 0.7 to 0.8 standard deviations, these estimates suggest that three years of charter school attendance for blacks would eliminate the black-white performance gap."
However, the same paper also says that at KIPP charter schools, "School
hours are extended typically to between 7:30AM and 5:00PM and include occasional Saturdays and summer weeks, and tutoring is also offered during these times." so I wonder to what degree the 'value added' by top charter schools comes simply from teaching more.
 Marzano, R. J. What Works in Schools: Translating Research into Action. Alexandria, Va.: ASCD, 2003, p. 7
 Kane, T., Gordon, R. and Staiger, D. Identifying Effective Teachers Useing Performance on the Job Washington, D.C.: Brookings Institution, 2004, p. 8
 Peske, H. and Haycock, K. Teaching Inequality: How Poor and Minority Students Are Short-Changed on Teacher Quality: A Report and Recommendations by the Education Trust. Washington, D.C.: Education Trust, 2006, p. 11