They allege they were abused by staff and other students at the school in Edmonton well over a decade ago.
One student claimed that she was sexually assaulted, became pregnant and had an abortion against her will.
Queen's Bench Justice John Rooke says in a lengthy judgment that too much time has passed to grant class-action status.
But he also says that if his decision were reversed on appeal, he would allow an action with several conditions.
Regina-based lawyer Tony Merchant, who specializes in class actions, filed the lawsuit in March 2008 on behalf of students who boarded at the school between 1955 and 1996.
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