What other boards should be on this list? ... How do they compare?
There are 2 wiki pages comparing the RaspberryPi that you can sort/read/improve;
The wikis are probably better resources as they can be updated with new products like the 4k/usb3 boards that are coming out now. Generally these are the popular options:
Popular Ultra low power micro controller is the advantage of the arduino-micro($25). Arduino has 19 other official boards.
Popular Inexpensive full fledged computer(Linux, 1080p video, 35,000+ applications) is the advantage of the raspberrypi-a+($20). Raspberrypi has 3 other official boards.
Inexpensive USB3 speed on a full fledged computer is the advantage of the ODROID-XU3 Lite($99). ODROID has 4 other options.
Inexpensive 4k video is offered by ODROID-C2 ($40).
Where do these boards leave off and vendor specific evaluation board begin?
If your doing any large volume work you would use an "evaluation board" then order many chips to put on your own boards.
... suitability for training kids?
select popular open source so there will be many options for them.
There are new options every year, some of them may meet specific needs better than the products listed, but this overview should give you a general idea of what to start comparing.