The Meanest Girl, by Debora Allie, 2005

Alyssa's best friend Chelsea's got no excuse for inviting Hayden, the meanest girl at PS 58, to her birthday slumber party, but she goes ahead and does it, and that's just the beginning of her odd behavior, leaving Alyssa confused and mad. And what's gotten into her sort-of boyfriend, Dillon? And who's leaving weird stuff in her locker? And what if cute Mr. Carter reads what she's written about him in her English class writing journal? Sixth grade is pretty hectic, and it's hard to chill, but a little bird teaches Alyssa a thing or two. Fun middle-grade realism. Recommended.