For privacy reasons figures were not provided for schools with less than five suspensions (Solway and Makoura Colleges). The ministry figures show none of the five suspensions at Rathkeale resulted in exclusion or expulsions during the last 18 months.
Mr Kersten said one of two of the recorded figures concerned resuspensions, so the true number of students suspended was less than five. "We're not comfortable with one suspension. I'd like to think we do a lot of work with our boys and families to get to a point where suspension is not required, but at the end of the day it's not a perfect world that we live in."
Suspensions were appropriate in some cases for the sake of other students, he said. "If it constitutes gross disobedience and you're just not making any headway with that child, or if it compromises the health and safety or learning opportunities of other students, then, yes, it'll happen."
Post Primary Teachers' Association president Angela Roberts said suspension numbers alone did not accurately reflect whether a school was doing the best it could.
"I think in general it's fair to say most school boards do their best to support students to remain in school so suspension by and large is a last resort."
However, she would like to see more resourcing from the Education, Justice and Health Ministries to enable schools to act as "hubs" with support for vulnerable or at-risk pupils.
"Teachers are teachers - they're not drug counsellors and nurses or all those other things. They're not the police, they're not judges, so it would be fantastic if schools got the support they needed to enable teachers to get on with teaching."
Principals' Federation president Phil Harding said the number of suspensions was troubling, but problems in schools were a reflection of society. Marijuana use was unremarkable in some high school settings, for example.
"Sometimes people see schools as being apart from the rest of the world. Well, they're not - they reflect the worlds in which they live."
Mr Harding said the education system needed to change the ways it kept problem students engaged.
He did not see the need for an independent review of suspension decisions.
Having sat through several disciplinary hearings, he knew boards were not out to "flip kids on a whim". - Additional reporting by Nicholas Jones