A maths teacher confessed to having a year-long affair with a teenage student after her own daughter reported her to police, prosecutors say.

Alberta Padilla, 52, started a sexual relationship with the 17-year-old boy while she gave him personal tuition at the Lady Bird Johnson High School in San Antonio, Texas, it is claimed.

Ms Padilla allegedly had sex with the teen in a public park and bought him gifts including food, clothes and a mobile phone after they started meeting to have sex.

She was arrested and charged with forming an improper relationship between an educator and student after her daughter raised suspicions about the affair with the police, according to local news station KSAT.

Ms Padilla faces up to 20 years in prison if she is convicted.

According to an arrest warrant affidavit, one of her daughters had recorded the alleged victim asking her not to tell the police about the affair.

He allegedly said he had developed feelings for Ms Padilla.

Ms Padilla was arrested on Thursday on suspicion of forming an improper relationship between an educator and student and is being held in Bexar County Jail after bail was set at $20,000.