Horatio Chapple, 17, was on an adventure holiday to the remote Svalbard islands in August 2011 with the British Schools Exploring Society (BSES) when he died.
The Eton pupil, from Salisbury, Wiltshire, was sleeping in his tent when the bear went on the rampage, inflicting fatal injuries to his head and upper body.
Trip leaders Andrew Ruck, 27, of Edinburgh, and Michael Reid, 29, from Plymouth, were also injured along with pupils Patrick Flinders, 17, from Jersey, and Scott Bennell-Smith, 16, from Cornwall, before the bear was shot dead at the camp site where they had been staying.
Horatio's parents Olivia and David Chapple yesterday told an inquest in Salisbury they had been concerned about polar bear attacks before the expedition.
They thought the teenager would have a working trip wire around his camp site and a device that would shoot flares up to 50 metres to frighten approaching bears, but only team leaders were equipped with them.
There was also a shortage of tripwire, stakes for the tripwire and the device's trigger, as well as mines to be placed around the site.
Mr Chapple, a surgeon, said: "We believed that the staff at BSES would do as they said and act responsibly to protect the children under their care.
"We were never told the bear trip wires only sometimes work. The risk assessment refers to flares being available to all members of the expedition.
"If this had been implemented then Horatio would have at least had some time to defend himself other than with his bare hands."
Mr Chapple also said a risk assessment suggested that a bear watch would take place.
A report by High Court judge Sir David Steel that was published to coincide with the inquest found the BSES should have had such a watch.
Mr Chapple said he had previously discussed with his son how to handle a polar bear attack .
The inquest heard the threat of serious injury from a polar bear was assessed as being three on a scale of one to three while the risk of encountering a polar bear was two out of three.
"No parent or nobody would want to go on an expedition where a risk was categorised as likely yet the planning wasn't there.
"I believed and trusted the things that were listed, otherwise I wouldn't have let him go."
His GP wife added: "I had no idea how a campsite should be set up at that stage. I didn't know there was the possibility that a trip wire may or may not work. I didn't know they were so fraught with difficulty."
Richard Payne, chief leader of the expedition for BSES, said trip wires had first been used at camp sites in Svalbad on a previous summer expedition in 2010.
"My intention was that all young explorers and leader would have a pen flare," Mr Payne told the inquest.
"It was only when we landed at base camp, which is 40-50km from the airport, that I discovered there weren't enough pen flares to equip everybody on the expedition.
"I took the decision that I would equip the leaders of each group and the doctors with pen flares."
Mr Payne said he had changed the original trip wire from fishing line to a heavy-duty braided fluorescent cord as the previous system was "going off too easily".
Equipment for the trip wire was put into a box along with four tonnes of equipment, which was loaded on to a vehicle and then a boat without being checked, he said.
When the box was unloaded the day before Horatio and the rest of the expedition arrived, equipment for the trip wire was found to be missing.
Mr Payne said the camp sites were changed to be triangular in formation to make up for a lack of mines, with Horatio's group having three mines instead of four situated around their site.
Mr Payne said the lack of mines was the only aspect of the planning he was dissatisfied with.
The hearing continues today.