Student or Learner
I think it's an idiom.
What does it mean? Is it fairly common?
I don't think it is an idiom per se. Rather it is a slogan to attract someone's attention. I believe it is a title of a book on being a volunteer or attracting volunteers. Is it a common saying...not where I come from in Canada. Perhaps it might be in the USA when it comes to serving their country. I could see it as a slogan in a religious context as well.