system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are so many public elementary/middle/high schools in America still based on an agrarian (9 month, Sept to June) calendar as opposed to a year round calendar?

It just seems to make sense to switch.
gpt
It's a settled cultural concept, and we've built everything around it. The "cost" of changing would be far greater than any benefits.

For example: many kids get summer jobs. This not only provides them with income but also work experience. A lot of conventions for teachers, educators, kids, etc. are scheduled for the summer.

In addition, the summer is sort of a "safety valve" for all sorts of things. Teachers who need to take classes, or kids that need to take summer school to "catch up."

Finally, even though it has agrarian roots, we've molded modern society around it. All sorts of industries rely on the concept of the "summer vacation," and for a lot of them it makes economic sense to capitalize off of huge amounts of visitors concentrated in a three-month period. 

*Could* we change it? Sure, we could. But why? The system in place works pretty good.