DCPS projected an enrollment of 47,247 students for the 2011-12 school year when it put together its current budget. And through the uniform per pupil funding formula, which provides a minimum of $8,945 for each student, that’s what the school system received.

But this week’s audited enrollment showed DCPS with 45,191 students, or 2,056 less than forecast. That means the system got $18.4 million for new students who are either ineligible for residency reasons or who never materialized.

So is the refund check to the D.C. treasury in the mail?

Not likely. DCPS routinely--some critics say systematically-- overestimates enrollment projections built into its annual operating budgets. In FY 2010 and 2011 the system also received more money than it would have if payments had been based on actual enrollment: a total of $29 million, most of it in the area of special education, according to research by the staff of the Public Education Finance Reform Commission (PEFRC).

Not so for D.C.’s public charter schools. While DCPS is fully budgeted in the spring on the basis of enrollment projected for the following school year, charters receive their allocations on a quarterly basis, beginning July 1. If audited enrollment falls below spring projections, allotments can shrink in the third or fourth quarterly payment.

PEFRC staff report that public charter schools collectively would have received $5.2 million more in FY 2010 and FY 2011 if they had been budgeted on projected enrollment instead of actual audited numbers (On the other hand, schools that under-project get more money).

This was an issue raised by charter representatives to the commission, tasked by Mayor Vincent C. Gray (D) to study equity issues. Three members — Allison Kokkoros, chief academic officer for Carlos Rosario PCS, Irasema Salcido, founder and CEO of Cesar Chavez PCS and Jeremy Williams, director of business oversight for the D.C. Public Charter School Board-- recommended that ultimate funding for both DCPS and charters be tied to audited enrollment. But their position made it only as far as PEFRC’s draft minority report.

Enrollment is, as DCPS spokeswoman Melissa Salmanowitz said this week, “a moving target.” On Feb. 14, according to the enrollment and attendance database, the system was serving 46,512 students. That’s still 735 less than the spring projection but 1,321 more than the annual Oct. 5 count that was the basis for the enrollment audit. Enrollment historically rises after Oct. 5, she said, and DCPS receives no extra money to support it.

Salmanowitz didn’t say this, of course, but the implication is pretty clear: DCPS overestimates in the spring as a hedge against its post-Oct. 5 arrivals. Charters are not legally required to accept new students after Oct. 5

“We make our best effort to project an accurate number of students that will be enrolled in school,” Salmanowitz said. “The audit released isn’t 100 percent reflective of the actual number of students in the classroom at this moment.”

Where do the additional DCPS kids come from? Salmanowitz said officials identified four different groups: charter school transfers, new students in the high school STAY programs, students new to the city and students returning to schools with newly renovated buildings.

There is widespread speculation about whether some charters “dump” problem students into DCPS after the October count, although not a lot of hard data to settle the question. According to PEFRC the D.C. Public Charter School Board estimates that total enrollment decreases during the year by 0.5 to 0.75 percent, or about 150 to 225 students--not exactly a handful, but also not boatload.