Here's the Princes Highway route SE to NW in a 3590 which displays School Zones a little differently to the 3597 on the screen only. There are no Cyclops or Custom POIs in the unit. Note that when the time is manually set to a later time in the morning the alert is not given.
The information is clearly drawn from the map and the alerts are triggered by if the unit's set time falling within the start and end times of the School Zone activity. Also works in 2xx5. 2xx0 or 37x0 yet to be tested. I haven't got it to work in a 52 or 1350 so i guess the function is not supported in xx or 1xxx's firmware and therefore probably not supported in any earlier unit firmware either, but i'll check further and also report on other units soon.