Here is a powerpoint writing activity that I put together for my mixed grade MS afterschool class.

I told my students that we were going to write letters of introduction to an 8th grade class in Chicago (not really true). 

The following powerpoint explains the basic layout of a letter, and then includes examples from other students around the world in order to give students some inspiration.

I had students write at least 5 sentences in their intro letter, then draw a picture and share with the class.

Good luck!