Allegedly the problem was that parents had to quit their jobs to adjust to the schedule. To me this seems easily solved by having little Jimmy walk or take the bus to school. No need for parental involvement in those cases as 12 year olds are capable of getting off and on a bus without supervision
I used to work in Boston Public Schools, so I have some context that may or may not address your point. One issue is that for the most part, Boston does not do "neighborhood schools" anymore. So a kid could easily have a 1.5 hour* walk to get to school. However, your point about busses largely stands because, at least for high school kids, the district mostly partners with public transit to bus the kids around.
* Downtown Boston is tiny. But the actual official city is pretty big, and dips much further south than many people realize.
It is more because older children can watch the younger ones after school. A 15-year old can watch the 8 year old for an hour or so after school. the 12 year old might be able to, but can definitely stay home alone. An 8 year old needs care. The later start minimises this with a "traditional" work schedule.
Im sure google has precise answers and it has changed since it became a standard arguement 30+ years ago, but I do imagine plenty. 3 years between kids and having 3 kids gets you pretty close (the 8 year old would have a 14 year old sibling). I personally have siblings 6 and 11 years younger than me. The bigger issue with me answering is that not only am I 40, but I'm childless and living in a different country than I grew up in. I*m not sure what the standard family actually is right not in different parts of the country.
