DENVER -- A geography class at East High School almost got an anatomy lesson by mistake when a porn film was accidentally played in class.

According to the school, the mix-up happened Thursday when the regular teacher was out of town and a substitute teacher was trying to find a movie the class was supposed to watch.

"A substitute teacher was having difficulty opening a computer presentation that was supposed to be shown to the class. While opening what was thought to be the correct file, a pornographic movie started to show on the screen of the computer. The movie was on the computer screen for just a few seconds," Principal John Youngquist said in a letter sent to all parents.

Approximately six students may have seen the computer screen while the porn film was playing, he said. The movie was never projected overhead to the entire class, Youngquist said.

There were 23 students in the advanced-placement class, made up of freshman and sophomores.

The incident was reported to the school administration immediately.

"The students who may have seen the DVD were spoken with and their parents were contacted prior to the end of the school day yesterday. The physical and emotional safety of every student is of great importance to us at East High School and we will continue to work to provide the most effective learning environment for every young person," Youngquist said.

The Denver Public School District is investigating, said district spokeswoman Lourdes Souss. She did not know what disciplinary action will be taken, if any. She also did not know if the regular teacher -- who was out of town for a conference -- is back at work Friday.