I thought that ecology might be an interesting topic to teach using Scratch or Scratch Jr. so I was looking for an example. Of course, I found one right away. When I looked at this code written by a grade 6 student I got distracted by something else. I LOVE how simple it is to code multi-threading in Scratch. For me this was a 3rd year university topic but kids do it in Scratch (or likely Scratch Junior) without even thinking about it. It makes me wonder if Scratch may be a useful tool in teaching more advanced topics. In this case you could start by showing the Scratch code which is super easy to visualize before beginning to teach threading in another language.
I have been thinking this would work well in high school for a concept like looping.