This lesson teaches about some basic programming constructs using one of the simplest programming languages. Many students will have been exposed to it, so if it’s not for your crew, skip it. There are enough advanced options that a student can make a very complicated program. I think of it like legos – it’s a good space to play around and get familiar with the basic programming concepts.
Here are slides that can be helpful in introducing this topic.
Here is a link to my explanation of the Astronaut reaction time game. The tutorial suggests that you use the older version of Scratch on your Pi, version 1.4. It can be done with that or else you can use the slightly slower version 2.0. Version 2.0 is identical to what you find when you use scratch in a basic computer browser. It is Flash-based and it runs a little slower than version 1.4.