In my school you are not allowed to hold an entire class after the bell
rings (except for periods preceding a recess or lunch). All sorts of
complications arise when the kids are late to their next classes or the
school bus. Recently I had a small piece of clay sculpture (being used as
an example for the project) stolen off my cart during a class. When I
confronted the class at the end of the period everyone denied taking it,
although many of the children had seen it during the class. I wanted to
keep the class until I got my sculpture returned, but I had to let them go,
even though it was at the end of the day. Many have to catch a school bus
and have other committments that precluded my punishing the entire class
for one person's crime.
The shoe idea or other collateral seems like a better idea because it deals
with individual students rather than the entire class.
A pat on the back is only a few centimeters from a kick in the butt.