They probably got away with it because they were dealing with kids who could be fooled or intimidated into accepting any and all excuses why they were not being paid

. It probably took a parent or other adult to start asking questions about this to have it blow up in their faces.
Most assignments I take now I get paid at the game. But some house leagues I have worked elsewhere paid once a month, so accurate record keeping is vital to ensure your cheque has the correct numbers on it come pay day.