He has joined the campaign for higher safety standards following an incident in which one of his pupils was seriously injured.
Rigorous standards that apply to journeys during the school day do not apply before or after school, he told the Educational Institute of Scotland annual conference in Dundee last week. The union lent its support to a plea for escorts.
Mr Finn, who is also education convener of the General Teaching Council for Scotland, explained that a first-year pupil fell from a side window of the upper deck on the bus home, suffering head injuries.
Inaccurate press reporting had not helped the school and its community to cope wth the incident, he said.
"Eighty pupils leaving the school on that day were on the bus with one driver, with three pupils to two seats.
"During the same week, 80 pupils were leaving the school in two buses with eight adults, with a series of risk assessments established, with clearly established safety guidelines and first aid provided.
"I ask you, if it's safe during the day, surely it must be safe during the mornings and evenings in similar circumstances," he said.
Mr Finn added: "I would not wish to mislead you by suggesting that the security of pupils will necessarily be improved by bus escorts or the incident I'm talking about would have been prevented, but we need to start looking at this issue and the Scottish Parliament is the place to do that."
The injured boy is now back at school.