In a response to Education Week's article about expansion of charter schools below is a spot on assessment as far as I'm concerned. The title of the news article is Published Online: July 5, 2012

Prominent Charter Networks Eye Fresh Territory

This is the comment:
"Some teachers and administrators in charter schools may be doing great things (and some are doing terrible things), but scaling up the number of charters has broad ramifications, including the de-stabilization and possible destruction of American public education. 

There are numerous ways in which the high-intensity charter schools that serve low-income students have wound up with a more select group of students than that served by public schools serving roughly the same population:

1) Fewer students with disabilities 
2) Fewer students with serious disabilities
3) Fewer students with serious behavior problems
4) Students come from the more motivated/better-resource families among the overall low-income population--parents with the wherewithal to find out about the new school and the motivation and resources to put in an application for their child.
5) The high-intensity curriculum weeds out weaker students--they either self-select out or, in some cases, are pushed out.

Some of the charter chains have received massive financial support from private philanthropists. 

A 2010 article noted that nonprofit networks of charter operators such as Uncommon, KIPP and Aspire Public Schools — "have created only about 350 [schools] in the past decade, and required $500 million in philanthropic support." Some KIPP schools spend 50% more per pupil than comparable public schools.

With better resources and a more selective student body, it is no surprise that many charters boast better test scores. (Of course, many charters are at the bottom of the barrel in test scores, and scandals have plagued the for-profit charter world) 

However, as the charters expand, private support will be spread more thinly and the student body served will become less and less selective.

Given that average charters currently do no better than average public schools on test scores, it's reasonable to predict that simply expanding the number of charters will lead to a situation in which the average charter does noticeably worse than the average public school. 

Given that public school teachers are generally paid better and have more job security than teachers at charter schools, an expansion of charters also means a further weakening of the middle class.

Individual charters here and there may be important laboratories for innovation, but when you look at the big picture, any dramatic expansion of charters probably weakens education and America. 

I ate my first McDonald's French fry in the 1960s. If even McDonald's can't consistently deliver hot crispy fries after all these decades, I can't imagine why anyone would think that market-based approaches would consistently deliver excellence in education, which is vastly more complex and filled with uncertainties."