Livingston ISD said 45-year-old Ryan Boyd was a school-based officer who worked at Livingston High School but was employed by the city.
The district said it reported the alleged relationship to police on May 1.
Boyd was then removed from the school and placed on leave.
Livingston police say he's since been fired.
After both investigations were completed, LPD was notified that criminal charges would be filed. On May 11, Boyd was terminated from his employment with the City of Livingston and immediately taken into custody by Texas Rangers.
Boyd has been booked into the Polk County Jail with an improper relationship between educator and student charge.