I am looking for a couple of nouns that describe someone who is noticably improving at some learning activity. If someone is just starting they are a novice or a beginner; at the end, there are various words (expert, master, etc.). I am looking for words for someone who is a beginner, but who is markedly getting better, and for someone who is not an expert but is approaching it. I already thought of improver. It doesn't seem very satisfactory; neither does trainee, which doesn't imply improvement.
For the not beginner, not expert, you could use 'intermediate'.
You can get inspiration from this list
The Dreyfus model of skill acquisition might be a useful scale.