I loved that part about Laura's teaching exam! It was so alien to me, and seemed so impressive that I accepted wholeheartedly that a 15 year old could teach school. And I had foolishly forgotten about reasoning from cause to effect, though that seems to be an overarching theme rather than specific schoolwork they do.

I hadn't thought about last books like that - I don't think I'm particularly interested in why they're last books as long as they are in some way a completion to the series.