What's good: It's a funny and entertaining read. The switches of viewpoint and voice between the four different girls, all interesting and likable, work surprisingly well, as do the variations in story format between straight narration, school reports, letters, chat room transcript, etc. The adults in the background of the story are positive and caring and involved. The girls' club rules are full of positive messages, though phrased in teen argot. If the girls' economic circumstances and friendship seems a little too good to be true -- well, I'm not going to complain about that. I imagine girls of just the right age and developmental stage will see themselves reflected in the characters. But some of that reflection, while a typical stage for girls to go through, is not exactly what I'd want a younger girl to start aspiring to ahead of time.
So what's not so good as role models for younger girls: One girl is extremely image conscious: her first reaction to people is to do a complete fashion inventory report card. One girl, out of a desire to retain her friends, does two things she has been explicitly told not to do by her father, violating conditions of their home rental; once this is eventually discovered, she gets off pretty easily, without any real penalty. One girl takes an approach with a crush that is tooth-grating for me: she spends hours primping, then maneuvers and tricks a (clearly not interested) boy into a date. Please -- how about an honest, straightforward approach to liking a real boy, and then maybe having a date -- not this attempted manipulation of a crush-object garbage!?!? The shallowness feels true-to-age -- but makes it perhaps a horizon-limiting, rather than an inspiring, example for younger girls.
I recommend for ages 11 or 12; iffy, depending upon maturity, for the younger "tween" girls of 8, 9, or 10.