A plus for Everyone!

I really dont think this is a good idea.
If a teacher were to tell me I have an A at the beginning of the class and I have already passed, sure that would be cool, but there is now no incentive for me to learn anything. Nothing. Maybe I'll listen in on a few lectures and do some work sheets, but whats the point? I've already passed, and I dont have to work for anything. This especially will not work with classes such as math, or science. In art, it is difficult to mark. Who's to say which is right? Or if its good enough or not? In subjects such as math and science, there IS a right answer, and there is a wrong answer. People will work hard if their grades depend on it. They will go out of their way to study for a test if they dont understand something so they will get it right.
For sure everyone wants an A, but it wont feel as good in the end, because they didnt work for it. And I can almost guarantee that no one by the end of the semester will know what is required for them to have an A.