(Photo by Krissy Venosdale)

By Meg Anderson, WAMU

Public school officials in D.C. need to plan for an additional 12,000 students in public and public charter schools in the next 10 years, according to a study released today by the Office of the D.C. Auditor. The number represents a 13 percent increase in enrollment, pushing the total number of students in the system to over 100,000.

The increase will not be distributed equally across the system, however, so budgeting effectively will require the school district to be better at predicting how many students will attend which schools, the study says.

The expected growth continues a decade-long trend. Enrollment has risen by nearly 21,000 students since 2008. Most of that growth — more than 18,000 students — happened at public charter schools. But the rapid growth in charters has begun to slow, and the auditor predicts that in the coming years, charters and traditional public schools will grow at the same rate.

Determining how many students will attend which schools — and how accurate those numbers are — will be key in making sure that the funding for schools is distributed appropriately.

D.C. Public Schools distributes funding on a per-pupil basis, and uses enrollment predictions to help decide everything from how many teachers need to be hired to how much money each school should have. The D.C. Public Charter School Board uses the enrollment projections when deciding whether or not to authorize new charter schools.

“It literally means how much money comes to your school,” says Eboni-Rose Thompson, a D.C. native and chair of the Ward 7 Education Council. “It has huge implications on the daily operations of schools because it determines their pieces of the pie.”

For the last five school years, just over a third of the enrollment projections made by DCPS were deemed accurate, according to the study, meaning that when the students were counted in the fall, the number was within 2 percent of the projection. Enrollment predictions at public charter schools were more accurate, with just under half of predictions meeting the standard for accuracy, but charter schools often have waitlists and caps on student enrollment that can allow them to be more precise.

Enrollment predictions can be tough for any school district. Changes to school catchment boundaries, school closures, consolidations, or even a city’s housing stock and economy can affect how many students will go to a certain school or stay at that school for the whole year. For example, current predictions for DCPS enrollment were the least accurate at schools where students are “highly mobile,” moving in and out of different schools frequently, the study found.

And a school district that also has the option of charter schools — like D.C. — can be even more complicated to predict.

“The degrees of complexity when you’re allowing school choice and also have a public charter school system leads to a lot of uncertainty,” says Steven Martin, a senior research associate at the Urban Institute. “[The District] has had their work cut out for them for years.”

But more school choice doesn’t necessarily have to mean less accurate predictions.

“The underpinning of a choice model is information,” says Mary Filardo, executive director of the 21st Century School Fund. “It should not be a surprise that a charter school next door is adding a grade.”

The study recommends a 15-step system overhaul for DCPS to follow in the future to predict student numbers more accurately. One of the key recommendations of the study is to maintain a central database where student enrollment is recorded in a consistent way. The study also recommended sharing 5- and 10-year estimates alongside the next-year projections and reviewing enrollment projections annually.

“More transparency and documentation will lead to more accuracy,” says Tracy Richter, president-partner of Cooperative Strategies, which has analyzed enrollment numbers for thousands of school districts across the country. “If those factors are better documented, it will narrow the margin of error.”

Along with the study’s recommendations, the D.C. auditor is also releasing an online database of school-level enrollment data.

This story originally appeared on WAMU.