Horatio Chappie, 17, was on an adventure holiday in Svalbard, northern Norway, when a bear came into the camp, took him from his tent while he slept, and killed him.
The incident happened in August 2011. Four people, including two teenagers, were also severely injured before goup leaders managed to shoot the 250kg bear.
The inquest on Monday revealed the trip-wire around the camp, which would have alerted the trekkers to the intruder, had been secured by a paper clip.
The British School Exploring Society, who were responsible for 73 children on the Arctic Circle trip, admitted a faulty wire was repaired using only a paper clip. They stand accused of ignoring safety standards set out by Norwegian authorities.
The inquest also found there was no bear watch on duty and the team were untrained in using rifles. During the incident a team leader was unable to fire the rifle as the bear attacked.
Sir David Steel, who wrote the report, criticised safety measures as 'inadequate', reported the UK's Daily Mail.
The parents of the dead boy were in court during the hearing.
The inquest continues.