According to a witnesses, the boy stood up about two minutes into the orientation session and stabbed the girl. The assault was broken up by a teacher.
The victim was taken by helicopter to OU Medical Center. Police said they took the boy to a juvenile detention facility.
The school's superintendent, Barry Gunn, said a teacher subdued the boy and took the knife. Other teachers gave the girl CPR while they waited for first responders.
Police said the boy used a folding knife with a serrated edge that was about four inches long.
Gunn said the school does not have a school resource officer, but they are in still in the process of getting one in place.
Counselors will be available on site at the school for at least a week.
Students' backpacks were searched on their way back into the high school. Parents arrived to pick many their kids up, but school is expected to continue like normal
Authorities said they did not know the relationship, if any, between the teenagers.