Scratch

I'm looking into using Scratch as part of a very basic class on programming and computer science, and it provides many of the basic imperative-style elements fairly well.  Despite that, the ability to declare and reference a function is one of the most basic ideas in CS and writing code.  I wanted to ask if there was anything in Scratch that would help students to understand how functions work.

Ideally, I'd like to have some kind of a value (oval) block, which would essentially give whatever the function returns.  The block would hopefully take a variable number of inputs (arguments), in addition to some way of indicating what function to use.  With an oval block, you could either use the returned value or simply ignore it and produce side effects (which is almost exactly like C).  Ideally a function could be made global and could be referenced in any sprite or object available.

I'm kind of guessing this isn't exactly possible the way I'd prefer to do it.  The "broadcast" ability would sort of work, but you'd have to set some variable as the arguments and then set another variable to get a return value.  Unfortunately, that's a rather indirect and difficult way to help a student understand the concepts of how functions work in most languages.  After Scratch, I'll likely go into something like basic Python or maybe even C, and knowing how to use a function is going to be absolutely crucial to learning good programming techniques.