This book is dedicated,"" with good reason, ""to all of us who have ever been forced to do something entirely against our nature because it was good for us."" And many a youngster, reading of Tuesday's child Grace's submission and impromptu rebellion, might leave it around for her (or his) parents to see. Grace is an avid baseballer, just about to get her longed-for chance to pitch, when her mother convinces her father that Grace isn't growing up graceful, and should take ballet lessons--which happen to be on the same day as local league-play. Grace, objecting, isn't unreasonable or unrealistic: she's ready to give up the tough non-baseballers she's been hanging out with (""I was surprised that my parents had let the whole thing go on this long""); realizing that her mother's made up her mind, she'd even be willing to give tap lessons a try. But her mother, denied-the-advantage of ballet lessons as a child, only suggests that she might do both. ""It was more important to her for me to take ballet,"" thinks Grace after that confrontation, ""than it was for me to be happy."" Accustomed to doing things well, Grace does try--and her schoolwork improves, her base-running benefits. But some steps she can't do; her best friend Byron, who has worse troubles, gets tired of her complaints; with no outlet except her father's unspoken sympathy, she grows morose. Then comes the ballet-school spring production of Peter Pan. Grace, a tall, sturdy girl, is cast as a little Bo-Peep doll, and ridiculously garbed. She considers, and rejects, the idea of repeating an earlier bike accident. But on stage, struck (not tapped) by the loathsome show-off Tinkerbell, Grace erupts, socks her tormentor, and doesn't repent. Nor need she; others have seen the provocation, and her mother recognizes her mistake. Baron, making her fiction debut (after Getting Started in Calligraphy), has given this the earmarks of a case history, with some pop-fiction trimmings--but she doesn't overdo in arty direction. Indeed, it's all adroitly plotted, and pleasing scene-by-scene.