My DD BURNED through the A to Z Mysteries and Capital Kids mysteries (same authors). Loved them both. She reads Magic Treehouse books, but she doesn't seem as enthralled with them.
She just recently started reading The Tail of Emily Windsnap and LOVES it (there are three in that series I believe). It is definitely more advanced than A to Z so I know she is okay with that (though I don't want them to be so advanced that she doesn't understand what she's reading).
Any serious favorites? She is almost 7 years old. She really seems to like getting into series because it makes her want to read the others. We have read the first couple from the Boxcar Children - I definitely want to delve more into those.
I know this has been asked before, but it seemed a lot of the series were centered around school. I'd prefer to keep the stories mostly away from school (don't care if they are actually school kids, just want the adventures to be not AT school).