Shall I Compare Thee to a BPS School?

We all know that when charter schools are compared to district schools, district folk cry foul. Arguing that charter schools "cream" the best students, or parents, or whatnot, they liken comparing BPS and successful charter schools like Boston Collegiate, Roxbury Prep, or Excel Academy to comparing apples and oranges. They argue that these comparisons make them look artificially bad, since their kids are harder to help to succeed to begin with.

I have two thoughts on this.

1) If successful charter schools were barely doing better than the district, I think this would be a better argument. However, successful charter schools are leaving BPS in the dust. I don't think that small differences in student populations can account for major differences in test scores.

Case in point: In 8th grade, 34% of BPS student scored Advanced + Proficient in math last year. Here are the percentages for some of the highest achieving Boston charter schools - Roxbury Prep (86%), Excel Academy (88%), and Boston Prep (93%). They're almost doing 3x as well. I doubt that those students would have been doing as well if they had stayed in BPS. However, I know that some people will never believe in the power of these schools if this is the argument that's put forth. So here's a more powerful one:

2) When the successful charter schools that I'm familiar with in Boston look at MCAS results, comparisons with BPS and the state averages are almost an afterthought. They assume that they're going to do better than these marks. If they don't achieve at this level, it's considered to be a major problem.

Instead, they compare themselves to wealthy, suburban districts like Weston, Wellesley, etc. They believe that only when urban students are consistently doing as well as their wealthy, white peers that we can start talking about the achievement gap being erased. (Whether test scores can really satisfy that condition is another story for another day.) However, I think everyone in urban education should cheer when schools populated with majority low-income and minority students are doing as well or better than kids in high-achieving suburban schools.

I think successful urban charter schools would be better served comparing their students to suburban schools than to their district peers down the street. I think it's a more compelling apples to oranges comparison, and it diffuses one of the main pillars of the creaming argument.