From the webpage:
About
Scala school was started as a series of lectures at Twitter to prepare experienced engineers to be productive Scala programmers. Being a relatively new language, but also one that draws on many familiar concepts, we found this an effective way of getting new engineers up to speed quickly. This is the written material that accompanied those lectures. We have found that these are useful in their own right.
Approach
We think it makes the most sense to approach teaching Scala not as if it’s an improved Java but as a new language. Experience in Java is not expected. Focus will be around the interpreter and the object-functional style as well as the style of programming we do here. An emphasis will be placed on maintainability, clarity of expression, and leveraging the type system.
Most of the lessons require no software other than a Scala REPL. The reader is encouraged to follow along, and go further! Use these lessons as a starting point to explore the language.
Excellent!