Thanks for the feedback. You're going to need to find or create alternate content for your classroom. Flash Player will no longer work after 2020, and most browsers will remove support for all plug-ins at that time.
For completeness, here's a link to the original announcement from 2017:
https://theblog.adobe.com/adobe-flash-update/
Here's a link to our FAQ:
https://www.adobe.com/products/flashplayer/end-of-life.html
HARMAN has an ongoing support program for Flash, post-2020, but it's very much not free. Sheppard Software could, in theory, engage with HARMAN to find a solution to keep their content working (most likely by packaging that content as a desktop application). It's possible, if your district manages individual computers like an enterprise, that you could license and distribute a maintained Flash Player from HARMAN to your managed computers that allows Flash to play the Sheppard Software content that's important to you.
More details on options for enterprise can be found here:
https://www.adobe.com/products/flashplayer/enterprise-end-of-life.html