A "more rigorous" roll check is now conducted immediately after lunch. But Mr Wood says that although such provisions might have highlighted Mike's disappearance sooner, it would not have stopped him leaving, despite the school being made aware of his troubled home life.
The inner-city school wasn't a "fortress or prison" and pupils often left its grounds, especially at lunchtimes.
On the afternoon of March 13, all students were involved in a group "alternative programme" activity, which meant the normal class roll wasn't taken after lunch.
No matter what systems were in place, there would always be occasions when the normal routine was disrupted, Mr Wood said.
"Mike would've known the programme for that day several days in advance so he may possibly have guessed that it was a good day to leave," he said.
Mike had been at the college for only two weeks after moving from Queenstown with his mother, and had kept to himself at school.
Police have referred the case to the coroner but are investigating what they call a missing persons probe.