D.C. school officials are investigating 118 special education students who might not live in the District but whom taxpayers are spending about $7.7 million on to send to private schools.

Under federal law, the District must pay to send special education students whose needs aren't served by their neighborhood schools elsewhere, often to private school. Between tuition and transportation -- school buses regularly transport students to Baltimore and further -- the average cost per student is $65,000 each year.

A report commissioned by the Office of the State Superintendent for Education has found that District school officials couldn't verify the residency of 118, or 7 percent, of the students, and officials are investigating whether families committed residency fraud.

Marc Caposino, a spokesman for OSSE, said he believes most of the students under investigation are boarders at private schools, which are as far away as Pennsylvania and as close as the Washington suburbs. That's why families could fake their addresses without school officials catching on. Because they live at school, those students cost more than average.

Special education students sent to private school accounted for 43 percent of the residency fraud cases under investigation this year.

"Five or 10 years ago, I remember people saying they were going to move to D.C. because they knew they could sue the school system to get their kids a quality placement in private school," said Yetta Myrick, the president and founder of D.C. Autism Parents.

But Myrick said she believes that the appeal of getting -- or faking -- a D.C. address has fallen as school officials focus on cutting the number of students in private placements. The city has said it has saved $40 million in the last year and a half by doing just that.

The probe extends beyond special education students: OSSE also is investigating 126 students enrolled in D.C. Public Schools, as well as 32 enrolled in public charter schools.

Non-resident tuition varies by grade level but can reach more than $12,000 each year. There were 72 students in DCPS or charters that were identified as non-residents at the beginning of the school year and charged $743,315. Only $156,006 has been collected.

Caposino said a simple "lack of payment" was to blame. Some parents withdraw their students when they get the bill, but never pay for the time their child was enrolled.

Schools are responsible for collecting non-resident tuition, but it becomes the responsibility of OSSE if parents refuse to pay.

"Education is free, but not without cost," State Superintendent Hosanna Mahaley said.

Of the students potentially committing residency fraud, most were in high school.

Tenleytown's Woodrow Wilson Senior High School had 37 students under investigation at the beginning of the school year. As names have been cleared or students have left, 22 cases remain.