This is a common question that I've heard in person several times, but it showed up in Blogmail for the first time this weekend. :)
First of all, in what I would estimate to be 80% of instances, your son knows exactly why he has a demerit; he just doesn't want to tell you why he has a demerit.
One of the funnier episodes of last year came when one of our boys received two demerits, and went to Mr. Tyler to ask why he received them. Since Mr. Tyler is a disciplined record keeper, he told the boy who assigned each demerit, what each was for, and when they were assigned by the teacher. The following day, Saturday, the boy came to serve his demerits, and his mother confronted Mr. Tyler wanting to know how her son was supposed to learn from demerits when he had no idea what he had done to deserve them. Mr. Tyler calmly turned to the boy, and asked him whether he knew why he had received his demerits. The boy, realizing that a trip to the Honor Council was on the line if he answered untruthfully, answered that he did know and told his mother the exact details of the demerit. Needless to say, the mother retracted her criticism of the system. :) Don't worry, a lot of MUS faculty and administration were boys ourselves long ago, so we know what parents have to deal with.
In the other 20% of cases, I do believe that your son doesn't know why he received a demerit, but the reason for that situation is that he was a combination of forgetfulness and laziness. When a teacher assigns a demerit, the student is told at that moment that they have received one. I've assigned probably four demerits in the past two weeks, and each one was clearly explained (no socks, no homework, talking in class/rudeness to a fellow students, throwing a projectile in the hallway).
Now, we are all aware that some things, particularly unpleasant ones, tend to slip a boy's mind. Each Thursday, in assembly, Coach Tyler in his stentorian voice announces that the weekly demerit list has been posted. He also says each week, seemingly unnecessarily, that anyone with questions about their demerit should come to his office and ask for clarification. And, each week, after the boys cluster around the demerit list to check their fate, some come to Coach Tyler for more details. Almost Invariably, the boy leaves the office having remembered the offense and its circumstances. Some plea for leniency, but Mr. Tyler explains that he is an administrator and cannot offer that; leniency can only come from the teacher who assigned the penalty.
Yet, there are still instances when a boy, upon being picked up from school on Friday afternoon and having to ask their parent for a ride to Saturday School the following morning, forgets why he must attend. I've seen enough boys to know that some truly have forgotten, even if they were told only the day before or a few hours earlier. More probably hope that temporary amnesia may shift some of their parents discontent toward the school and away from them.
Sorry, guys! Now your parents know the whole story.
P.S. We don't post offenses on the demerit list because we don't want to embarrass the offenders. I guess we could, but we'd probably get more complaints had we done that.