I was just looking through the Arcing thread and someone said that they thought Arcing was akin to "basic sentence diagramming" that they used to teach in school.
That got me to thinking about a piece of software that I actually paid for that's now being made available for free; it's called Koineworks. It's from Lexel software and it's a very interactive tool to explain and teach sentence diagramming. It has instructional sections, quiz sections, step by step areas...its' really a fine piece of software for those of us who are not Greek whizzes....I'm not.
I heartily recommend it.
here is the link