After teaching students some basics (stage, sprites, costumes, loops, movement, ask/answer, broadcast/receive, variables), I challenged them to create their own projects.
Documents with sample code for lots of Scratch implementations of APCS topics. I just finished using these with my APCS class (they have no prior programming experience).
In Germany, Ralf Romeike uses Scratch to introduce high school students to the joys of Computer Science. In his website, Romeike documents his teaching experience lesson by lesson.