Going to class is very different in America.
First of all you don't need to arrive in time. Being here at the beginning, 10 minutes late or 30 minutes late is the same for the teacher. This notion of respect doesn't exist in America.
During class if you need to go out or want to leave early, you just take your things and leave. The only thing that is forbidden is to disturb the class.
The class is very quiet, people are listening or on their computer but no one is interrupting the teacher. The students are very participating and give a lot of opinions during the class.
The dress code is also different, you can come with your pyjama, sport clothes or even keep your hat on - it doesn't matter.
Even in big class where there is 100 students, you can have little group project to do in the room, and every one is playing the game.
The relation with the professor is warmer than in France, even if in France they also help you, here they almost do the work instead of you when you ask it.
In one of my class the text grades were so bad so the teacher just said that she will give an extra point to everyone.
The tests are easier, it's most of the time multiple questions very explicit. You just need to read your notes once to have more than 60%.
Here they use an interface called Blackboard where they put all your grades, you can interact with the other students and the teacher for your group project. Also the Email adress is related a Gmail address which makes it easier to use Google Drive for the group project.