How not to play God in class

A student is messing around for the whole lesson.  Surprise, surprise, he doesn't finish his assignments and he wants more time. 
Another student works really hard on her assignment but can't quite finish on time.  She wants an extension too.

Would would you give the extension to?  Why?
My guess is you would base your decision on who you think made the most effort.

Next question: what gives you the right to judge effort?  Who made you judge, jury and executioner?  Who, in other words, made you God?

What if we decide to be honest with the first kid: "Paul, I don't think you deserve an extension because I think you wasted your time.  However, if you disagree, write me a letter telling me why you think you should have the extension."

In the end, it's still the teacher's decision.  However, higher purposes have been achieved: Does the teacher have the courage to allow a student's argument to sway her?  Does the student have the ability to argue his point rationally?  Does the student realise what he is asking for?  Do both have the ability to admit they can be wrong?