Why don't the first three Gospels all agree?

Now that Essay 2 for my New Testament: Gospels class is in the professor's hands, I thought I would share with you my effort on Essay 1.

Here's the assignment description for Essay 1:

As you are about to begin an adult Sunday school class, one of the participants approaches you and says, “There’s something I don't understand. When I read my Bible I can see that the first three Gospels are a lot alike, but not exactly alike. Sometimes one of them has a story that the others don’t, or one seems to have left out things the others have. Or they tell stories in different order. How did that happen? We say the Bible is the word of God, but if these Gospels don’t agree about things Jesus said or did, what are we supposed to believe?” You are someone who never passes up a “teachable moment,” so you decide to scrap your plans for the class and address this question, drawing on the best of your wisdom from your introductory New Testament class. Write out your response to your questioner.

I responded to this assignment in two parts. Part 1 was a "handout" for the class in the form of a parable, and Part 2 was the "presentation" or actual essay. (Sorry about the PDF format, but I'm just too lazy to bring 'em into HTML.)

If Essay 2 turns out not to have been an utter fiasco, I might post it too, eventually.