First I should let you know they were using play money to do this.Schoolchildren in Washington state have said their third-grade teacher forced them to pay to use the bathroom, which caused at least two children to wet their pants.
WA elementary school teacher accused of ‘pay to potty’ scheme that caused kids to wet pants
The teacher was probably doing this to try to teach them how to budget their money. Which is a good idea, however I don't think I would have included restroom breaks in it. If she was going to include using the restroom she should have let them go but if they didn't have the money possibly take away a few minute of their recess.
I'm also wondering what kind of treats they are getting besides popcorn. Maybe this is why so many kids are overweight.