Dallas ISD police say a middle school teacher was being blackmailed by a teenage student she was sleeping with.

Court documents show Thao “Sandy” Doan paid about $28,000 to the student after he threatened to tell police.

Doan taught math at Raul Quintanilla Senior Middle School in West Oak Cliff. She was arrested last Friday.

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The mother of the teen says she tracked the source of some suspicious text messages to a teacher, who she had met many times at school events and who taught her son math when he was in the eighth grade last year.

The mom reported the texts to the school, which called Dallas ISD police and removed the teacher from class the same day.

Nidia wanted to speak about her son as long as FOX4 didn’t use her last name.

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“This really changed my son,” she said. “This really turned my son into another person that he wasn't.”

Nidia says text messages, also quoted in court documents, tipped her off to her son's alleged blackmail of a teacher. She'd later learn the teacher is accused of having sex with her son when he was 14 years old.

“At times, he started getting into drugs, drinking, leaving the house. And he would probably get money and just leave the whole weekend,” Nidia said. “I wouldn't hear from him. I'd be out looking for him.”

Court documents say that Nidia reported the texts to school officials on January 10 and demanded that Doan stop giving her son money.

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