Long story short, my 17 year old is in Y12 6th form and has taken up a part-time job a couple of months ago. We very much encouraged this as they are financing a long trip abroad through school that way, for which they needed to fundraise (we are absolutely not in a position to contribute hugely to this).
However, they've gone from a point where they were stressing about school work every night (3 work-heavy A-levels) to apparently barely working on that anymore, while simultaneously working all the school-free hours under the sun.
They are working at least 4 days a week, usually evening shifts of 5-8 hours, and are rarely home before 9am anymore, often walking home for half an hour in the dark (due to buses not running). Working hours are ridiculous, for example, shifts this week have included working until 10pm Friday night and then working again at 8am the Saturday morning. All for minimum wage for a 17 year old. They've also been put on shifts Christmas Eve, Boxing Day and New Year's Eve and Day and appear to be on late 8-hour shifts almost every day of the school holidays.
Every time I have raised concerns over the hours (or told them they're working far too much, or got upset that suddenly we have no family time anymore whatsoever, or raised concerns over school) I've been met with "well, they just put me on these shifts even if I say I want an early one". My child is either unwilling (more likely) or unable to put their foot down and say no.
Grades in two of the subjects have not yet suffered, apparently (they still get As, or so they say), and the third one is coursework-based, so harder to judge on whether it is affected, but I know from experience that sixth formers barely get communication home regardless of their work and effort.
Where do I stand here? How much say do I really still have with a 17 year old who doesn't listen about work (we initially agreed to 3 days max a week - that lasted exactly one week), but just takes on any shift, and is barely home apart from late at night, who is tired around that all the time (no surprise) and where it is hard to gauge how much school is affected? Am I right to be worried about burnout? Do I just need to let them make their own mistakes and watch it all crash down in a few months?