How to Teach Your Students to Write Descriptively

I was in a grade 3 classroom a while ago and had the opportunity to co-teach a lesson with another teacher (which pretty much meant she led the lesson and I helped the students with it).  The aim of this particular lesson was to get students to write descriptively and here was how it went:

Prior to teaching the lesson to the students the teacher pulled me aside and told me that another teacher was going to come in all in a panic that a scary dog chased her through the school but wasn't going to describe the dog anymore than that.  

So this happened and she came busting through the classroom door and the students got all excited.  She told them about the dog and that the principal wanted them to make found posters for the dog so that they could find it's owner.  

All was going according to plan until one student freaked right out and dashed over to some counter height stools and climbed on top of them.  He was terrified of dogs (and it didn't help that the only describing words for this dog was that it was scary).  The rest of the class loved it but the one that was afraid I had to continually console him from off a tall table (that he tried sitting on multiple times) and their pictures all looked very different (which was the point of the exercise).  

At the end of the period the teacher confessed and told them that there was no dog and explained why it was hard to come up with an accurate poster for this found dog because we didn't actually know what the dog looked like!  

But alas, even with the confession the terrified student couldn't be convinced to leave the classroom.  So while the rest of the class went to music he stayed behind and read a book (at least he wasn't on top of the table anymore).  Eventually I convinced him to leave the classroom and walk with me to go pick up the class from music (and then it was the end of the day so he went home). 

So, have you ever had a lesson backfire in a pretty major way (even if it was just for one student)?

What are you doing to help encourage your students to add descriptions to their writing?

Here's another post I did about a project where students described a hero, here is what a grade 5 class did to describe hot chocolate and here is what I had my grade 8's do when describing how to make a sandwich.