In this assured debut, science whiz Libby Monroe shines when she selects Cecilia Payne, an astronomer who first determined the composition of stars, for an American History profile of someone excluded from the textbook. Like the author, 12-year-old Libby has Turner Syndrome, which means she has a single X chromosome, her heart is "three sizes too big," and she looks different from her classmates. Libby's intellectual curiosity already makes her stand out from her peers, but some elements of her condition, such as the fact that she wears hearing aids, make forming friendships difficult. She considers the library her best friend, until new girl Talia Latu moves to Colorado. Allen deftly sketches the dynamics of Libby's close-knit family, conveying Libby's anxiety when her older sister Nonny's pregnancy develops complications. To solve Nonny's financial problems, Libby dreams of winning the Smithsonian Women in STEM contest, which offers a cash award. Though a thread about Libby's contacting the textbook's editor feels tangential, it offers comedy and a lesson in disappointment and persistence. This witty novel's heroine proves winning, whether or not she gains top prize. Ages 10--14. (Mar.)

Libby Monroe is a seventh grader who loves science and has a habit of conversing with notable people in her mind. She also has an optimistic disposition and Turner's syndrome, a chromosomal condition found only in girls. Turner's syndrome causes many complications in Libby's life: her body has characteristics associated with it, so she is sometimes bullied, and she struggles with some skills, including interpersonal ones. Her family life is warm and loving, however, with her sister, Nonny, providing a huge chunk of support. When Libby enters a competition from the Smithsonian, writing a letter to introduce an unrecognized woman in STEM, she works hard not only on her entry about astronomer Cecilia Payne, but also on developing a friendship with a new student at her school. Libby's sparkling first-person narrative is directed straight at the reader, and her optimism is infectious. Allen has Libby convey information about Turner's syndrome without sounding contrived, since it's part of Libby's somewhat filter-less personality. All the primary characters shine in this impressive debut.