KELSO, Wash. – Authorities allege in court documents that a substitute teacher at Castle Rock High School exchanged about 100 text messages a day with a 16-year-old student, some of them describing sex acts he wanted to engage in with her.

The new information in the “sexting” case came to light Monday, the same day that the teacher, 27-year-old Dustin Matthew King, appeared in a Cowlitz County courtroom for the first time.

He had no comment while leaving the courthouse.

The Longview, Wash., man was arrested Friday afternoon and booked on suspicion of communication with a minor for immoral purposes, which is a felony.

A student tipped off school staff on Friday that the 16-year-old girl was receiving the text messages. Castle Rock police happened to be at the high school and questioned the victim and King.

The girl admitted to exchanging sexually explicit text messages with King for the past week, according to court documents. King also admitted to exchanging the texts, the documents said.

Castle Rock Schools Superintendent Susan Barker is trying to grapple with a situation district policy does not specifically cover.

“I’m always surprised when people that select teaching as a profession may get confused about a boundary,” she said.

School officials said King was an excellent teacher who substituted for several school districts in the area in the past and had a clean background.