I can't find that number either, and one of the few places that the edu-eMac is mentioned is here:
http://www.everymac.com/systems/apple/emac/stats/emac_1.25.html
There was a standard production 1Ghz model that used the older logic board with a 133mhz bus and had USB1.1. The uncataloged educational model was also 1Ghz but had the faster 167mhz logic board and USB 2.0 and, with newer RAM modules, can handle up to 2G RAM.
The best way to tell is to get the seller to run System Profiler and look at the Hardware Overview. If the machine ID says "PowerMac4,4" it's the older and slower standard production model. If it says "PowerMac6,4" it is the edu-eMac with the faster logic board and USB 2.0
If it is the faster model, check its serial number against this list before laying down any money:
G8412xxxxxx- G8520xxxxxx
YM412xxxxxx - YM520xxxxxx
VM440xxxxxx - VM516xxxxxx
Many eMac USB 2.0 machines in those ranges had a logic board problem that is, today, about as close to a fatal condition as you can get given the high cost of repair. If it's in one of those ranges, I'd walk away.