Increasing numbers of schools in the US are banning media players from exams following concerns that students are using them to cheat.

Mountain View High School in Idaho has already banned the devices, after teachers heard students discussing the use of media players to cheat.

"It does not take long to get out of the loop with teenagers," said Mountain View principal Aaron Maybon. "They come up with new and creative ways to cheat pretty fast."

The teachers feared that pupils were recording spoken crib notes, saving them as music tracks and propping their head up with one hand to conceal an earpiece.

Alternatively, answers were being written in the notes sections of legitimate music tracks.

Mobile phones are already banned from many exam halls as students have been found texting answers to each other.

These problems have been around for many years. In the 1980s a French student used a radio microphone in his sleeve to communicate to someone outside the hall with an earpiece concealed under long hair to hear the answers.

The pair were rumbled by a teacher who overheard the communications on a portable radio.