I went to a UK public school (for US residents, this is what you call a private school). Standards were very high. We had a teacher exchange with an inner-city comprehensive. The results were interesting. The teacher we got was extremely good. He held the attention well, he covered the material in a manner both interesting and comprehensive. However, he ran out material about 30 mins through a 40 minute class. Why? Because his lesson plans were from his old school, where lessons were a hour long, but he had to constantly stop to keep order. We didn't interrupt him, the class was just over half the size of his usual one, and he didn't have to do anything to keep us in our seats and focused on the class. As he put it 'I've got a lot more time to teach the same course. I can afford to take more questions and take time to help out individuals. I don't think you guys are any smarter than my usual students, but there's so much more we can do here.'