Can school lotteries make schools more diverse?

Last year, 48 percent of students attending D.C. Public Schools were at-risk, meaning they were homeless, in foster care, qualified for food stamps or TANF, or were high school students who’d been held back a grade. The share of at-risk students in a DCPS school varies greatly, from 1 percent to 90 percent.

DCPS students are assigned to a neighborhood school but school mobility is high.  In 2012, 43 percent of DCPS students attended their assigned neighborhood school.  For charters, though, there are no attendance areas.  So we wondered: can charter schools, which base admissions entirely on a lottery instead of a student’s address, better mix at-risk students than DCPS and create more egalitarian schools? Our answer is a qualified no.

Though charters last year enrolled about the same percentage of at-risk students as DCPS (44 percent), most charters (47 out of 53 elementary and elementary/middle schools) have lower concentrations of at-risk students than nearby DCPS schools serving similar grades—and by nearby, we mean within the same DCPS elementary zone. The difference in concentrations of at-risk students between charters and DCPS is greatest in areas of the city where high numbers of at-risk students go to school.  For DCPS schools where 75 percent or more students are at risk, the at-risk population in nearby charters is lower by at least 10 percentage points. In areas where DCPS schools have smaller at-risk populations, some nearby charters have at-risk populations closer to those of DCPS, while others have some of the lowest concentrations of at-risk students in the city. Charters tend not to locate near DCPS schools with the lowest concentrations of at-risk students.

(click to interact)dot graph 2

We found similar results when we plotted the percent of at-risk students in a school versus neighborhood home prices. In neighborhoods with the lowest home prices, charters have considerably smaller portions of at-risk students than DCPS schools. As home prices increase, there are charters that have at-risk populations more similar to those of DCPS schools, though other charters in these areas have very small at-risk populations. There are few charters in the areas with the highest home prices.

(click to interact)scatter plot 2

What does this look like across the city? The map below shows that the concentration of at-risk students in both DCPS and charters generally increases as you move from northwest to southeast (and here we show all schools, not just elementary and elementary/middle schools). West of Rock Creek Park, where the DCPS schools with the lowest concentration of at-risk students are located, there are no charter schools, and the charters with the lowest concentrations of at-risk students are located in the center of the city. East of the Anacostia River, charter schools tend to have lower concentrations of at-risk students than DCPS schools.

(click to interact)landscape

Put another way, both DCPS and charters have some of the least economically diverse schools in the city—they’re just located in different parts of the city.

least diverse

The map below gives you another way to see what’s going on in different parts of the city by comparing charters and DCPS side-by-side. The map is interactive and it lets you zoom in on different neighborhoods and filter schools by the size of their at-risk populations.

One thing that strikes us in the map is the marked difference in at-risk populations in charters and DCPS schools east of the Anacostia River. Since only two charter schools east of the river had more than 25 percent of their students cross the river to go to school last year, it seems likely that charters here attract non-at-risk students from neighborhood DCPS schools or keep non-at-risk students in the public school system who would have otherwise left for private schools or moved.

The map below also shows that in the north and northeast parts of the city, plenty of charters have at-risk populations similar to those of DCPS schools, while other charters have much smaller at-risk populations.

(click to interact)neighborhood-by-neighborhood

We’re curious to hear what you conclude from these graphics and what patterns you see that we may have missed.

What exactly is this data?

Data on at-risk populations is from the Office of the State Superintendent of Education and is for the 2014-2015 school year. Readers should note that some types of students that might seem at-risk might not be counted as such, including:

  • undocumented students who qualify for food stamps and TANF but do not receive benefits because of their immigration status;
  • adult students; and
  • students enrolled in alternative education programs.

School locations are from the Friends of Choice in Urban Schools. We define a charter’s “nearby” DCPS school as the DCPS elementary school for which a charter’s location is zoned in the 2015-2016 school year. The boundaries for the DCPS elementary school zones are from the Office of the Chief Technology Officer.

We have excluded from our analysis schools that serve alternative, special education, and adult populations.

Three charter schools in the graphics above closed after the 2014-2015 school year: CAPCS, Tree of Life, and Options.

Thank you to Yesim Taylor for her comments on this post.

17 thoughts on “Can school lotteries make schools more diverse?

  1. The most interesting conclusion is that there are several distinct regional school markets in a district as small as DC and they are interrelated with residential/class segregation. In each market you see different behavior. Charters are a “refuge” in Wards 7 and 8 but nonexistent in Ward 3. These markets should be the basis of analyses of charter-DCPS interaction, not a single, stark DC-wide analysis.


    1. Good observation. I added a graph to the post that shows concentrations of at-risk students by neighborhood home prices, which gives more data on how socio-economic factors are at work.


  2. This is interesting but I think what’s being done with the data isn’t the best way to answer the question asked in the title.

    The major constraint in terms of diversity in the DC public schools is the demographics of the school system overall. Maximum diversity to me would mean that each school was representative of the overall school system. Since this is looking at the at-risk category, that would mean every school has 48% of kids at risk. To compare charter schools to other public schools, I’d compare the actual representation to that idealized representation. This is the kind of approach that Simpson’s Index takes, and it’s a common one for assessing intra-system diversity.

    A slightly different approach would instead use different numbers for the charters than the public schools (44% for the charters, whatever the relevant number is for the non-charter publics.) The results shouldn’t be that different.


    1. Yep, one way to measure diversity is to see how far each school is from the 47 percent mark (which is the percent of at-risk students system-wide), and if you do this you will that charters are more diverse. In other words, charters have fewer extremes than DCPS. This is actually how I approached the analysis when I first started it. But then when I threw geography into the mix, and found there were quite a few charters with relatively low at-risk numbers in areas where DCPS schools had at-risk populations near 50 percent, my takeaway was charters aren’t creating as much diversity as you’d expect for a 100% lottery system. I think plenty of people will instead conclude that charters increase diversity–a totally reasonable conclusion. It’s interesting to hear which way people fall. Thanks for writing! ________________________________________


    2. Accidentally pasted a link in my comment. Was trying to say if you look at how far schools are from the 47 percent ideal, you’ll find charters are more diverse. ________________________________________


  3. I would like to see a comparative analysis of the performance of DCPS school with high levels of at risk students EOTR against charters with equally high at risk students. For example, Democracy Prep has 70% at risk population and King has 88%. How are they both performing? Can King learn from Democracy Prep, what innovations can be shared or explored?


    1. I should have said in my apply above what is Friendship PCS doing since we have some data on them and not much on Democracy Prep since they are newer to DC. Friendship PCS Southeast has a student population that is 72% at risk.


  4. Great analysis. It seems to me that open enrollment practices are having a normative effect whereby charters’ composition of at risk students are more like the citywide average than the local in-boundary DCPS school. If there were charters in Ward 3 and west of the park, I would imagine that the percent of at-risk students would be higher than their DCPS counterparts.


    1. That is one way to look at it. Charters have fewer extremes (low and high concentrations of at-risk students) than DCPS. ________________________________________


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