One of the most interesting parts of being a coach developer is seeing other people put on session's. Having the opportunity to observe other coaches regularly allows me to see the art of coaching in a completely new light. Deciding what a successful session looks like requires context and consideration for a lot of variables. That being said, there are a few things in particular that will stick out as good indicators.
The Topic Comes Out In The Game At The End
There's no better feeling than working on a topic or theme for the evening and seeing a player "get it" or put it into their own context and use it in the game at the end. For me, that shows a transfer of learning and an understanding of not only 'how' to do something, but also 'where' and when'. When I see this within other coach's sessions, I get just as excited about the fact that the session struck a cord with their players.
Successful Check For Understanding
A useful way to see if your session has been successful is to check for understanding. There are a number of methods to do this varying from; "Robbie, can you show me?" to "Summarize in a sentence how we build out from the back?" If a coach can test their players at the end of a demo, an activity or the entire practice, potentially you can gauge how effective the coaching has been within it.
For a closer look at check's for understanding, take a look at: Four Types Of Questions To Try Whilst Coaching.
Gameday Transfer Of Learning
This is possibly the most rewarding measure of success for a coach. A successful transfer of learning to gameday is the sole reason coaching exists: to teach players the game so that they can play it and apply it without us. The end goal should always be to get to the point where the players don't need us any more. Gameday, at the youth level, should focus less on winning and more on development so that players have the opportunity to demonstrate what they've learnt and make their own decision's. If your player's can implement what you've worked on that week, several days after you taught them, you know you're doing something right!
Ultimately, the best way to measure your success as a coach, is over a period of time. Coaches that flit from one club to another will rarely be able to measure their success. Those that have stability and a long term approach to development will be able to see the fruits of their labour. While not the only ways to measure success or effectiveness, checking for understanding and seeing a transfer of learning to games will surely act as good indicators for any coach.