I think one of the best ways to help kids understand specific writing techniques, such as "Show, Don't Tell" - is to present them with examples of before and after revision.
Over the years, I've collected some great samples of revisions done by fifth graders that illustrate their grasp of the "Show, Don't Tell" technique.
Check these out (from workshops in which the kids - fifth graders - write biographies of a parent or grandparent):
Before: Bob wasn't happy when his father told him they were moving.
After: Bob's father came in and announced, "We're moving." Bob groaned when he heard the news.
Before: John loved to play baseball with the kids in the neighborhood.
After: As soon as John got home from school, he dashed back to his room to grab his baseball mitt, then hurried to meet his friends in the vacant lot next door.
Before: She was good at swimming.
After: Swimming medals covered her bedroom wall.
Before: Sam loved to go to the Cape every summer with his family.
After: Sam counted the days until his family would load the beach chairs and boogie boards into the car and head for the Cape.
Before: He hated doing chores, like vacuuming, washing dishes or raking.
After: He groaned when he had to vacuum. He whined when he had to wash dishes. He grumbled when he had to rake.
Before: His favorite subject was geography.
After: He loved it when the teacher whacked her pointer on the map, pointing out countries and rivers.
For any kid who didn't quite "get" Show, Don't Tell, hearing these usually lights the old proverbial light bulb for them.