Could you provide context? Are they considering this for elementary school students, or for highschool students? Public board or private board? Are they currently only teaching for 6 hours a day (ie, something like 9 am to 3 pm?) and which changes are they considering making (ie, 8 am to 4 pm)?
A link to a news article or document would be great.
For elementary schools, I can REALLY see the 8 hour school day being a problem -- you're cutting into extra sleep time, professional development time, possibly intramural sports/activities time, certainly clubs/after-school events time, marking time, social time... etc.
For highschools, on the other hand, in Ontario here they're already balanced so class starts at 8 or 8:30, roughly, and it's done between 3 and 3:30... for that age group, it seems to work just fine.
The QUANTITY of the in-school hours isn't nearly as important as the QUALITY of what' being taught during the hours available.
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