Montgomery County police and the boy's parents described the investigation Tuesday at a news conference, the Washington Post reported.
Yee Tak Sharon Kui, 25, of Rockville, Md., allegedly had sex with the 15-year-old at his parents' home while they were at church, investigators say. She taught at the Frost School, a private special education school in Wheaton.
Investigators said Kui faces charges that include sexual solicitation of a minor and sex abuse of a minor. According to court documents, the boy's parents discovered in mid-November that Kui had sent him sexual text messages.
Kui realized she was likely to be arrested when a supervisor at the Frost School suspended her, WUSA9.com reported. She apparently made arrangements to leave the country, the report said.
The boy's father said his condition means he feels emotions deeply but has a hard time expressing them. He said he and his wife searched for a long time before they found a school they believed could meet their son's needs.
"This was a particularly disturbing case. Our victim is a child, and a child of special needs. He should have been nurtured and protected by his teacher," an official said.
Kui graduated from the University of Maryland in 2011, the Post reported.