The text message said, "Lockdown in place, armed intruder on school grounds". Mr Campbell, who was away from the school at the time, said staff were told to lock doors and keep children inside.
Police confirmed they went to the school after a member of staff received a text with "concerning contents".
Mr Campbell said the school was in lockdown between 1:30 and 2:15, and began to contact parents.
"We had to treat it as though it was real, and we did. We needed to inform parents of what was happening and why. When you say we're in lockdown mode because there's an armed intruder on the premises, it doesn't take long for parents to get very worried."
He said it was beyond belief that an example text would contain a message with such serious implications without any indication it was false.
"It was perpetrated by the people who are supposed to communicate effectively with our parents. You would think if you were sending out a test text that had something like this, that you'd put 'test text' in front of it, or you might say 'the magician has arrived'."
He said the school uses the company to link with its student management system, which is primarily an early notification that enables the school to quickly contact parents about pupils who are absent from school or if the school doesn't know where the pupil is.
Mr Campbell said the school was able to get messages to parents quickly, via the school's new app, as well as bulk emails and bulk texts, saying everything was okay.
He said police congratulated the school on its handling of the situation.
"We did the right thing, and you can't take any chances, but it's frustrating we received a text from an organisation that is supposed to be working for us."
A spokeswoman for School-links said the company was "very aware" of what happened and was investigating.
"We are looking into it."
Additional reporting by David Haxton of the Kapiti News
