Programming concepts
With Scratch, we'll learn how to turn our imaginations into games, stories, and animations, and in the process, we'll learn some common programming concepts. If you're already a knowledgeable programmer, then you'll find out what Scratch has to offer your students.
The Scratch team publishes several resources to help educators, including a Programming Concepts guide, which I've summarized below:
Programming limitations
As of Scratch version 1.4, there are a few limitations with the language. As taken from Scratch's Programming Concepts guide, here are the concepts Scratch does not cover: functions, recursion, exception handling, file input/output, inheritance, parameter and return values, and defining classes of objects.
If that last paragraph sounds like gibberish, don't worry about it.