Finn said investigators had completed reports highlighting some areas of concern.
He was seeking explanations from principal Chris Grinter and deputy principal Fred Whata. They were due to respond within two weeks.
It is understood three families whose children were excluded from the school's Tai Mitchell Hostel complained about unfair treatment.
One of those students, Chris Reid, 17, believed he was targeted after making friends with boys whom he claims the school did not like.
Reid said he was aged 15 when he was first randomly called from a classroom and brought into another room.
There, he was asked to strip to his boxers and urinate into a container - without his mother's consent. The test produced a negative result.
"I felt disgusted," he said.
He said the process was repeated on three more occasions including once when he had only just gone to the toilet.
On that occasion he said he was forced to stand in his boxers for more than 90 minutes and drink up to 15 cups of water until he could urinate.
Reid said all but one of the tests produced negative results. The fifth was positive and showed up cannabis smoked after the death of his father.
His mother Mary said her son was told to leave the hostel late on a rainy night. She had been interviewed by the ministry's investigators.
The Herald on Sunday understands the school nurse refused to carry out the drug-testing of students about a year ago after becoming concerned they could be illegal. House masters had been instructed to carry them out since.
Another parent said his son was sent home after about $900 worth of drugs was allegedly found under his pillow last year while he was not present.
The businessman said 14 hours passed before the school asked his son to take a drugs test and told him of the find. The boy's father said another three hours passed before he [the father] was notified.
His son denied all knowledge of the drugs - yet was immediately excluded.
He said he had asked for the police and school board to be involved in investigating the allegations but this had not happened.
A month after the suspected drugs were found, he received a letter from the school which stated the drugs had been finally handed to police.
On following up with police, he said he was told they did not have the drugs.
Rotorua Detective Senior Sergeant Mark Loaper said there was a "long delay" before the matter was brought to their attention "and it wasn't from the people that should have brought it to our attention".
He said police had since spoken to the school and had been speaking with ministry investigators.
Finn said he was aware of the allegations put to this paper but would not comment in detail.
He said the ministry was concerned about the allegations and "that's why I'm there to deal with it".
Education Minister Anne Tolley said: "Parents don't want drugs in schools and schools should be addressing this issue in a proper manner."
Grinter refused to comment yesterday.
Whata could not be reached for comment.
