Deputies say that the investigation began after they received a complaint by parents who said that Day was having inappropriate contact with their son.
Authorities say the teen's parents told investigators that they found text messages and nude photographs on their son's cell phone.
Investigators say they determined that Day and the teenage boy had already had sex, and that they had made plans to meet at her home to have sex again on Wednesday.
“This is a classic case of a serious breach of public trust. School teachers are entrusted to protect and educate our children, not to engage in an unlawful sexual relationship with them,” said Canadian County Sheriff Chris West.
Authorities with the sheriff's office used the boy's cell phone and pretended to be him while contacting Day. Investigators asked Day if the meeting was still on, and she allegedly said it was but added that he should hurry before her husband got home from work.
Day texted the teen's cell phone that the “door's unlocked as usual,” and investigators found Day sitting on the living room floor with the lights turned off and candles lit.