Everyone understands the concept of a school bus. But Karlsruhe even offers school trams. From Mondays to Fridays, special tram-lines 16, 17 and 18 run to and from the European School in Waldstadt. Only pupils of the ES are allowed onto those trams.
DWM GT8 No. 210 is just entering the stop "Elbinger Straße Ost".
Frankly, there should be more cooperation between school districts and transit authorities in the US. The average school bus gets used perhaps 3 hours a day. A district that needs some income could certainly run their buses on public revenue routes when they're not shuffling students around.