I am often asked as an Agile Coach when I know that I have been effective at my job. The answer is simple- my work as a coach is done when the team in question is capable of being predictable.
And what, you may ask is predictable? For me it is a team that is capable of consistently delivering 90% or greater of points that have been planned for an iteration. I have given this capability a name. I call it the Gold Standard.