As I’ve discussed in several recent posts, I’m increasingly concerned with how charter school expansion has played out both in our cities and in our suburbs.
My one post that perhaps best captures my overarching concerns is here.
It seems that increasingly, no matter where I look, my worst fears are realized. As I’ve explained numerous times – I began my work on charter school policy with positive expectations. Not so much anymore. Here’s how it’s all playing in Jersey City, NJ.
First… the map…where we have our two highly skimmed schools – Soaring Heights and Learning Community Charter. 
And yes, we do have some charters for the commoners at least in terms of income status.
NOTE: While LCCS has not updated its latitude/longitude data for its new location – the enrollment data characterizing their actual student enrollments are from 2012-13.
The skimming behavior of the elite charters not only disadvantages other district schools, but also those charters for the commoners.
Perhaps more problematic than the number of lower income children left behind in district and non-elite charters is the number and share and type of children with disabilities. Here are the aggregate shares, which are disparate enough.
More problematic however is the fact that the big red bar representing district schools includes much larger shares of children with far more severe and more costly disabilities. Charters are serving only those children with the least severe a) mild specific learning disabilities, b) speech/language needs and c) in some cases “other” health impairments.
And under New Jersey’s persistently biased growth measures, these strong patterns of student sorting not only have consequences for the average level of student performance, but also for the average gains. Clustering more disadvantaged peers together – which necessarily happens when you cluster more advantaged peers together – has consequences.
Higher poverty settings have lower gains and vice versa. Does this mean, as NJDOE would have us believe [by arguing that their growth measures fully account for student background and that teachers are the most important in school determinant of growth], that teachers in Liberty Academy and Jersey City Comm Charter suck and teachers in Learning Community and Soaring Heights are awesome? This is a highly suspect (read totally ridiculous, offensive and asinine) conclusion to draw.
And lower performing settings have lower gains, though this picture is somewhat less clear, because Soaring Heights fails to soar to its expected heights.
The sorting induced by some though not all charter schools in Jersey City raises concerns about how New Jersey charter policy should move forward in the future. This is not to suggest that any and all sorting is bad and should never occur – or be immediately stopped. But, we cannot ignore it… nor should we let the system run wild on its current path.
School Finance 101 
There may be another layer of granularity needed here to properly compare the special-ed populations. You appear to be assuming that all special-ed students assigned to the district are being educated in general-ed district schools. I do not know enough about JC to know the specifics, but it is a common practice in NJ for districts to send their toughest cases to private or public special-ed schools rather than try to educate them in general-ed district schools. I think the correct comparison would be the charters vs. individual general-ed district schools rather than charters vs. the district as a whole.
Both the regular ed school site or districtwide comparisons are relevant but serve different purposes. While you are correct that many NJ districts send out high need special ed students, the district is responsible for paying the high price of that tuition. To the extent that charters siphon off lower need students, the district is left to figure out how to cope with its increased remaining concentration of higher need students, contracted out or not. As for performance comparisons… yes… the impact on performance is best determined by looking at school level special ed populations… but NJDOE does not provide school site enrollment by disability type data. However, one can plot the % non-proficient special ed students using NJDOE report card data.