PLANO -- A Plano high school teacher was arrested and charged with sexual assault after police say a relationship between her and a student began on Snapchat.

The 16-year-old student told police that he wrote his Snapchat user name at the top of a test while in 23-year-old Alaina Ferguson's algebra class at Plano Senior High School, according to court documents.

Ferguson replied via the social media app, and the two met a few days later and had sex on a park bench in Lewisville, the teen told police.

Documents state that one to two weeks later, the teen and a friend came to Ferguson's apartment in McKinney that she shared with her fiancé, who was away for the weekend. Ferguson and the teens ate pizza and played beer pong, the teen said, and he and Ferguson had sex while his friend took the dog for a walk.

"Ms. Ferguson told [the student] that she knew it was not the right thing to do, but it felt right at the time, and that she was going to break it off with her fiancé because she didn't feel anything with him," court documents state.

The teen and Ferguson had sex in the same apartment on several occasions during their relationship, he told officers. The most recent occurrence was in the back of his pickup truck after a football game on Nov. 4.

Documents state that Ferguson gave the teen alcohol and the two exchanged nude photos via text messages during their relationship.

Ferguson was booked into the Collin County Jail on Nov. 30 on a charge of sexual assault. She was released Dec. 1 after posting a $100,000 bond.

The Plano Independent School District said Ferguson was hired in August of this year and resigned in October.