I re-read my post and realised that I didn't really answer the question! :P
For my kids, I know that they know if they have put in their best effort. Sometimes results don't show because of 3rd party influence. (eg. having a very strict, or demanding teacher/ examiner), or the environment. If I praise them for something which is done just for the sake of completion, they know I am not being truthful.
So in our family, we celebrate the effort of accomplishment, regardless of the results. This based on my assumption that everyone wants to do well in something that they are good at. For things that they are not good at, the effort of just trying is good enough for me.
