The Quadra 840AV was the last and greatest pre-Power Mac. I have one that still runs, but I have little use for it anymore, which makes me a little sad. It was really my best Mac ever, in the sense that it was once top of the line, had groundbreaking video capabilities, and made me feel like I could do anything.
Your 840AV isn't worth more than a few dollars in the market anymore. Since almost every pre-Power Mac (Motorola 68K-based) application can also run on Power Macs, there isn't much need for pre-Power Macs, even this, the fastest one.
It can be used for the tasks that any old Mac (or PC for that matter) can be used for, i.e., non-CPU-intensive applications like word processing. If you have enough RAM, you can do web surfing with an older browser. If you have a network, maybe it could run firewall software.
I doubt schools would want it as a donation. The schools I've worked with don't have much use for machines that old. For example, it would likely cost more to buy a Mac serial interface printer to use with a Quadra 840AV than a much better USB printer for any new Mac, so why bother? That's the trouble with very old Macs: they may still work, but its not worth putting more money into them.
I'm afraid that the Quadra 840AV is ready to take its well-deserved place in the computer museum.