The girls - aged 15 and 16 - were on a trip to Belize when a man talked his way into their cabin and raped them, and one of their friends, while their teacher and two minders slept a few yards away.
The former pupils, now in their twenties, had claimed six-figure compensation from the school, in the Medway area of Kent, and trip organisers, Adventure Life Signs, over the 2005 attacks.
According to a report in the Telegraph, they claimed not enough was done to protect them by the adults there to ensure their security.
But defence lawyers insisted the adults could not be held responsible for a rapist's crimes or for the consequences of a forbidden drinking session late at night.
And a High Court judge agreed. Mr Justice Mackay decided that the three "highly responsible and experienced adults" on hand could not be blamed for what happened.
Although the girls had not "positively invited" the man - who was the resort owner's son - into their jungle cabana, the judge said they "did not actively protest" to him coming in after they spotted him "lurking" in nearby trees.
They drank with him when they knew that was against the rules .
They all knew that he had no business to be in their cabana at all, let alone at midnight, and that they had no business to be drinking rum as some of them were," the judge added.
The third "highly intelligent" girl, the oldest in the group, did not join the other two in the High Court action and gave evidence that she did not blame the school.
She said she had coped with the trauma by simply "not talking about it" and pretending the attack never happened.
Exonerating the school, along with the trip's organisers - Adventure Life Signs Ltd - the judge said the whole ethos of the expedition, for which the girls had raised thousands of pounds themselves, "was not to crowd the girls with adult supervision."
Mr Justice Mackay added: "The party was continuously supervised by three highly responsible and experienced adults."Short of posting a guard on the door of each cabana, or instituting some system of watch-keeping, there would have been no way of defeating this man's assault on these girls, which he and up to a point they were at pains to keep from the leaders. "It would not fair, just and reasonable to define the scope of their duties so as to require them to make taken those or any other precautions that night."