Mind you wouldn't the 9-to-5 commuter and school journey have always clashed in the morning? A commuter journey would probably want to arrive in the city between around 0830 and 0900 - the same period the school journey would want to arrive at school. Or did many schools used to start after 9? Mine (in the 80s) always started at 0845, in the height of the commuter peak.As with most things in life, there isn't one single, simple answer, but from some old timetables, it must have been reasonably common for peak / spreadover buses to be able to do a works journey (or maybe even 2), a peak journey for '9 to 5' workers, then a school journey (and a similar afternoon combination although not always in the same order.)
Many of the workplaces that warranted works buses aren't there any more, schools seem to have drifted to earlier starting hours so school pupils end up travelling round the same time as the '9 to 5' workers (and there are not so many of them now), and many school journeys are now that much longer in distance and time for a handful of reasons, so can take up the whole morning peak for one bus.
A bus that can carry 2 or 3 good loads twice a day, and has the works traffic maybe 48 weeks of the year (allowing for works holidays), is more viable than one that only gets one full load twice a day and then for 38 weeks of the year (allowing for school holidays.)
Works journeys certainly seem to be extinct though I remember noticing a lot of them on old Southampton city timetables from the late 70s and early 80s.