What happens if the kids didnt show up for Saturday Detention?

I always wondered about that, never having been to Saturday Detention at all or in general, just basically had only a few minor incidents in school and never got into trouble (Didnt get get much) etc.

But what would Vernon have done if the kids had not even bothered to show up at all? Or worse came in an hour late because it was Saturday and were used to sleeping in and not going anywhere all day, like so many kids do? Lots of high school kids might just decline to show up for Saturday Detention at all because it is their day off of school, or even better they have a job where they work after school and they work early on the weekends because they dont have to be at school for those two days.

So it wouldnt be suprising if the kids just forgot to show up or refused to show up at all, claiming that they had a job on the weekends like McDonalds or bagging groceries and thus couldnt make detention without getting fired or into trouble at work, Vernon would have to take it, young teenagers usually dont care anyway and that would be obvious to most teachers in high schools.