The Luckiest Girl by Beverly Cleary (1958)
At home in Oregon, Shelley had not been in this blissful state. She had grown tired of going steady with her friend Jack, and tired of having everything decided for her: especially that she must wear the pink raincoat with the black velveteen collar that her mother had bought for her, instead of the yellow slicker she wanted. So when she was invited to spend the coming school year in southern California, Shelley's parents decided the change would be good for her. And now, just as she had been sure she would, she had found the boy she had always wanted to meet.
Their romance, however, is only one part of this funny and tender and wonderful book. What follows it is even more enchantingly gilded with a lovely light--the very shine of youth. (from the inside flap)