Charter schools are often criticized for under-enrolling students with disabilities.  For example, a report last October from Mark Weber (Jersey Jazzman) and Julia Sass Rubin (founder of Save Our Schools-NJ), both of Rutgers University, claims that

 Charter schools across the state do not enroll as many students with special education needs as their host districts (9% vs.15%). The classified students who enroll in charter schools also tend to have less costly education disabilities. This leaves their host districts with the task of educating both higher percentages of classified students and of students with the most costly needs. 

However, Marcus Winters,  in a new report called “The Myth of the Special Education Gaps,” looks closely at data from New York City Public Schools and Denver Public Schools to dissect enrollment gaps among students with disabilities. Here he explains the statistical  variations between enrollment of students with severe disabilities in charter and traditional schools:

 The paucity of severely disabled students in charter schools is often highlighted in public commentary on the special education gap. It is true that district schools enroll significantly larger percentages of students with relatively severe disability classifications than do charters. As shown in Figure 1b, the share of students with autism is 0.2 percentage points smaller in charters than in district schools in Denver and 1 percentage point smaller in New York City. Results for traumatic brain injury are similar. These differences do not contribute substantially to the overall special-education gap, however, as the percentage of students with severe disabilities is very small in both sectors.

Regarding students classified as having speech and language disabilities (the bulk of classifications), the biggest gap, Winters finds, is in kindergarten. He writes,

I suspect that the kindergarten gap is driven primarily by the fact that school districts often provide speech and language services to students in need of them prior to entry into kindergarten, and the parents of such students are reluctant to switch to a charter school, thereby interrupting the continuation of these services. As a result, parental choices contribute to the creation of a special education gap at the very beginning of formal schooling.

After kindergarten, the gap shrinks, at least in NYC and Denver. In fact, “in both cities, students with existing IEPs are significantly and substantially more likely to remain in their kindergarten school if it is a charter than if it is a district school. In Denver, four years after entry in kindergarten, 65 percent of students with IEPs remain in their original charter school, compared to 37 percent of students who began in a district school. In New York City, four years after entry in kindergarten, 74 percent of students with IEPs remain in their original charter school, compared to 69 percent of students who began in a district school.”

Read Winters’ whole analysis. His conclusion is clear:

The conventional argument that charters enroll relatively few students with disabilities because they “counsel out” special needs students after they enroll is inconsistent with the enrollment data. In fact, students with disabilities are less likely to exit charter elementary schools than they are to exit district schools. More students with IEPs enter charter schools in non-gateway grades than exit them. Of course, I do not mean to imply that no student has been inappropriately removed by a charter school because of his disability. But the fact that students with special needs in charter schools are less mobile than those in district schools suggests that such incidences are not widespread. Policies meant to address the special education gap that focus on the movement of students with IEPs are unlikely to be productive.