The Importance of Being Polite

I am very big on making sure that my children are polite to others. This includes saying please and thank you when they want things and when they have received help. It seems to me like, a lot of people don't do this anymore. I believe that teaching your children to be polite, is in its own way, teaching your child to be tolerant and patient of the world around them. If they can be polite to people regardless of how they are treated then they will become stronger adults.
      My children go to a private  school on the weekend. And I volunteer to help with lunch and other things, and it is very sad, that very few of these children are polite. When they are served they don't say please or thank you, they just take as if they are owed something!
 This make me so sad because these children are so smart but if they don't learn to be polite they will have lot of problems in their life. Is it the schools job or the parents job to teach children to be courteous?