It is very interesting to read about Lawrence Kohlberg's theory on morality. It seems to make sense to me. Children often do things or do not do things because they either want to be praised or not scolded by our parents. Children would only eat cookies before dinner if they thought they could get away with it (maybe they shouldn't mess with Arnold). Otherwise, they would not eat them before dinner. Not because society places any kind of pressure to not eat cookies before dinner, or because there is actually something wrong with eating cookies before dinner, but because parents will get upset if a child spoils their dinner. This is all it truly boils down to.
As pre-teens and teenagers, we often don't do things because of rules placed in society. These may or may not be arbitrary. However, this conventional morality often never leaves us. I have a good example of a person who only had progressed to conventional morality when they should have been postconventionally moral. My senior year of high school, I severely sprained my ankle during my final football game. We were deep in the playoffs, so most people in the school had seen it happen. I went to the emergency room immediately after the game and was on crutches the remainder of the weekend. On Monday when it was time for school, I decided I didn't want the crutches, even though my ankle was in severe pain. I didn't honestly want to deal with taking the elevator more than anything. Anyway, I went to class, but was a few minutes late. The teachers that stand in the hallway to give students tardies let me pass because they had seen the game. They just told me to get my ankle healthy. When I got to class, my teacher asked where my crutches were, as she had heard about my injury too. She said she wished me good health, however, she said that I was tardy for class. She made me walk to the end of the hallway with a bum ankle and get a tardy. Now, I realize I am biased, but was she justified in doing that? I was a senior, well respected in the school, was on track to be valedictorian of my class, etc. I wasn't being tardy because I didn't want to go to class, I was recently injured. Was she justified in doing so, or was she just being strictly conventionally moral?
I think she was being conventionally moral. You did not have your crutches so she could have been under the assumption that it wasn't a major injury and since you were late, she just went with the rules; tardy->punishment. Under my assumption of her thoughts, I think if she had let you in, then she was favoring you for all the good qualities you had. Other students might not like that. So as a teacher, what she did was right!