A teacher at an Arizona charter school has been caught by a principal having a sexual encounter with one of her students in her classrooms.

The school's principal, Leonard Miller, reportedly had suspicions that something improper was going on between the American Heritage Academy's biology teacher, 34-year-old Emili Kay Daniels, and her 17-year-old student.

Miller told the Yavapai County Sheriff's Office that he went to check on the two, but the classroom door was locked. When he unlocked the door, Miller said he saw Daniels and the student near Daniel's desk, and the student's underwear was exposed.

Daniels and the student at first denied there was anything sexual going on between them, but the student later admitted to sheriff's deputies that he was having a relationship with Daniels.

The student said their encounters went back to October 2008.

Sheriff deputies are looking at the two's cell phones to review text messages they may have sent each other.

Daniels was arrested on Thursday. She was booked on three counts of sexual conduct with a minor, local television station KTAR reported.