This past spring, I did a composition project with my fifth graders on Garageband to really explore the concept of chord structure and progressions. We found Beat Blocks to be a very useful tool to allow the concepts to receive the focus and not the small details that get in the way so easily. As a class, we walked through how chords are built as well as put together to make progressions in current songs and classic rock songs.
I am attempting a "blended classroom" lately, so my students all had access to these video tutorials in case they had questions, needed to watch a part again, or wanted to try it out at home. Here is the tutorial that shows the addition of Beat Blocks into the third stage of the composition.