Ms Schooner said her 10-year-old son was part of the school group, though he was not attacked.
“He said that bear ran so close to him, but it was going after somebody else,” she said, adding that “he even felt its fur”.
In a statement to the BBC, British Columbia Emergency Health Services said two people were critically injured, two more were seriously hurt, and seven others were treated at the scene.
Patients had to be transported to a nearby airport so they could be airlifted to the closest hospital, officials said.
The group were from Acwsalcta School, which is run by the indigenous Nuxalk Nation, in the town located 700km (435 miles) north-west of Vancouver.
“Officers are armed” the Nation wrote on Facebook. “Remain indoors and off the highway.”
“It’s hard to know what to say during this very difficult time. We are so grateful for our team and our students.”
The Nation’s officials have temporarily shut the school, offering counselling services.