Hi Eric,
Thanks so much for reaching out and for your interest in our products!
One way that you can achieve the results that you are looking for is to assign a category to each high school. This way, they will only create events associated with a category, which you can then display via a shortcode with Events Calendar PRO.
You can limit admin capabilities to your users with the addition of a third-party plugin, such as Members, so that they can only access the content that you want them to have access to.
I hope this helps to clarify things for you! Please let me know if you have any other questions!
Thanks,
Jaime