He said one or two were stuck hanging upside down on the Power Surge ride while it was stopped for about 10 minutes.
Although he was not at the scene, Bentley said teachers waiting at the bottom of the ride while the kids were being lowered believed there had been a malfunction.
"At no time did our boys or staff see anyone spitting," Bentley said.
The group were quite some way off the ground and the wind was quite gusty.
He said the boys were told by staff "we're going to get you down", and no one at the scene heard any mention of spitting.
"I'm incredulous. There was no warning. None of our boys heard an announcement, nothing was said to anyone there," Bentley said.
He said even if students had been spitting, they shouldn't have been left dangling by the fun park.
"I take real exception to the way it was dealt with."
After reports by other media this afternoon that the ride malfunctioned, Rainbow's End tweeted that it was deliberately stopped mid-cycle, "due to children spitting, having ignored previous warnings."
Rainbow's End chief executive Chris Deere said the ride was stopped and children were lowered manually from it after they had ignored a request by the operator over a public address system for them to stop spitting.
"I've spoken to both the ride operator and the supervisor that went down there."
He said maintenance personnel were called to the ride to manually lower it and let the occupants off.
"There was no mechanical issue with the ride."
Deere said after the group was removed from the ride, other people were allowed on it and it remained open for the rest of the day.