In most of the United States, participation in anything after school depends on a car. The arrangements that supply those rides are informal, unpaid and fragile.
The gap the carpool fills is structural
School transportation generally serves the regular day. Practices, rehearsals, tutoring and jobs finish after that service ends, and public transit is limited or absent in much of the country.
So the transport system for everything beyond the school day is a set of private arrangements between families, with no coordinator and no fallback.
It works well enough to be invisible, which is why the absence of a formal system is rarely treated as a policy problem.
Districts count buses and routes for the regular day and generally do not measure what happens afterward, so there is no figure describing how many students the informal system carries.
Coordination is unpaid labor with a known distribution
Someone tracks schedules, negotiates who drives which day, arranges cover when plans change and manages the social obligations that come with asking repeatedly.
That work falls disproportionately on mothers, and it is the kind of labor that is only noticed when it stops, since success looks like nothing happening.
It also has to be reciprocated, which means participation requires a household able to take its turn, in a car, at a specific hour on a weekday.
Failure is concentrated, not random
Households with one vehicle, with shift work, with a parent working evenings, or with no licensed adult available cannot reciprocate reliably.
Those households are gradually excluded from arrangements without anyone deciding to exclude them, because the arrangement depends on an exchange they cannot sustain.
The exclusion is also silent, since a family that stops being asked has no notification and no one to appeal to, and the student simply appears to have lost interest.
The effect on activities is selective
Activities with late or variable end times filter hardest, and those are frequently the ones with the strongest links to later opportunity, including competitive teams and advanced programs.
Students then appear to have chosen less demanding options, when the actual constraint was whether an adult could be at a curb at six o'clock.
What actually substitutes for it
Activity buses running a late route are the direct replacement, and they cost money and are among the first items cut when a transportation budget tightens.
Scheduling activities within the school day, or clustering them so one trip serves several students, addresses the same problem without new vehicles, and both are decisions a district can make.