Most schools I imagine. Often, it's used for extreme truancy issues, i.e. in the State of Texas, you have to be present a certain number of days I believe per school year.

So Saturday detention tended to be a thing you'd get sent to if you had a truly outrageous number of absences.

I believe there was a way for situations like serious illness where this rule doesn't apply. But let's be honest, most situations of excessive absences that I saw back in High School were NOT that.

In that sense, your kid isn't really being "punished" by receiving Saturday detention. It's just, the school doesn't have to advance them to the next grade level either if they missed like half the school days for the year and are under the minimum attendance. Like it or not, education in the United States is compulsory and part of that is that there is usually some kind of attendence policy. If you don't like it, then you can homeschool.