I'm talking about the bare minimum. I've seen maybe two or three blog posts (on agents' blogs) about how YA stories should focus heavily on the MC's internal journey, and how external circumstances should really be there to cause some kind of growth by the end. I always thought that kind of thing was a staple of coming-of-age stories, though :S

This is from Lauren Ruth's blog:
I would reject it because [character name] has no internal struggle and doesn’t appear to face the same challenges that teens face. All the conflict is external and I like to see interplay between external and internal conflict in YA.
Does this mean that agents prefer novels where there's a fair focus on the inside of the character? Most of my stories focus on external circumstances and only touch on the MC's internal issues when something major comes up, like friction between the MC and another character or issues with the love interest. I've never really given much thought to weaving a significant internal arc through any of my stories...