Based on my understanding of the history of the summer break........your former colleague had the break based on agriculture, where most of us do not.
In reading a discussion of this issue by Malcolm Gladwell, it is suggested that the summer break in fact had little or nothing to do w/agriculture.
Rather, it came out of current thinking at the time of the advent of public education (mid-late 19thC) that it was possible to over-work the mind, that too much study or concentration was bad for you.
A break based on agriculture would have been afforded in spring (plow and plant season) and late summer/early fall (harvest season).
There is no justification for a July break based on agricultural need.
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In terms of changing school buildings to offer A/C this is something we already need to do.
It is already very possible for June and even September to be oppressively hot.
New schools have been built w/air conditioning in Ontario since about 1970.
That means somewhere in the range of 25% of schools are fully air conditioned.
https://globalnews.ca/news/4429319/schools-air-conditioning-poll/
Note that parents agree and want a/c across the board even if the school year remains unchanged.
Much like accessibility, this is something that must happen, even thought it will be expensive and take time
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As for the resort/cottage sector, note that my proposal actually only shaves one week off student time off over the course of a year.
I am, however, suggesting 2-3 weeks come out in summer, in favour of a 1-2 week break in the fall, and maybe an extra week for spring break.
However, if you really want to boost cottages and resorts, the answer has almost nothing to do w/student time off; it has to do with parent time off.
Very few people send their kids to Deerhurst alone, or the cottage alone.
They go as a family.
That limits them to parental time off, which in Ontario is quite low vs world norms.
Stepping paid vacation up to 3 weeks minimum (or even 4, like Australia, New Zealand and the EU) would do far more to help this industry than an overly long summer break for students.