The act went awry and one girl was left in a four-hour trance after the show. Five other students were in a daze and 13 reported feeling nausea and headaches. The young hypnotist had to bring in his mentor to snap people back to normal.
The school provided an update on their situation Tuesday.
"There were fortunately no bad effects," said Daniel Leveille, the private school's director-general, at a news conference Tuesday attended by administrators, parents and students.
"Nevertheless, we believe in retrospect we should have examined this event more closely because of the hypnotic component involved. The fact that people aged 14 and younger are more susceptible to this type of phenomenon was not brought to our attention before the event.
"That's why we didn't ask for parental consent for the activity, which seemed until then to be a humourous entertainment event that was presented in Quebec high schools."
The school also elaborated Tuesday on events that led to the incident.
The student council at Sacre-Coeur had apparently asked for the act to be booked after hearing about its popularity when it played other schools.
"We contacted a school in Sherbrooke where the act had taken place so we could check its content," said Leveille. "Since everything went well, we approved the students' request without further consultation."
Leveille said everyone is back to their old selves. Lynda Beauregard, the chairwoman of the school's board of directors, said the school checked up on everyone.
"In recent days, our administrators have contacted the parents of all the students who were affected to make sure everything is well and to reassure them," she said.
Leveille said 450 students between the ages of 13 to 17 years attended the show at the school in Sherbrooke, about 150 kilometres east of Montreal.
Myrianne Cloutier, the mother of one of the affected students, says she's satisfied with the way the school handled the incident.
"Since the event happened, the school has contacted us several times to get an update on our children. I believe the institution acted promptly and professionally and did nothing wrong in this matter. College du Sacre-Coeur, as always, has my full confidence."
Emilie Lussier, the deputy prime minister of the student council, wasn't losing any sleep over the incident.
"We feel that we were treated to a good show despite some minor discomfort felt by some people," she said. "We shouldn't dramatize the situation any more that it has been."
-With files from Lise Millette