"We are very conscious of what is said and how suicide prevention is treated but the focus of this documentary was bullying and not suicide.
"This is how bad it can get because of bullying. It is saying we need to take it seriously because this can be the outcome."
One student told the Herald on Sunday she was upset by the documentary but no complaints had been made to the school.
"We have now had this concern expressed and we will look further but we would hope that if someone was concerned they would come to us and talk about it," Gunn said.
Year 12 teacher Chantelle Fisher said she discussed the documentary with the class.
"It was an upsetting documentary but we were not focusing on the suicide," Fisher said.
"They are year 12 so it is an age level that is appropriate."
Gunn said parents were not told the documentary would be shown in class as it had screened on TVNZ a year ago.
"This programme was on TVOne and I think at 8.30pm, so for 16 to 17-year-olds it is not unreasonable. "
The documentary was part of the "Keeping Ourselves Safe" programme that identified different types of abuse. It included bullying and self-defence lessons.