Till's Christmas

``Tacky'' is the word Matilda ``Till'' Wyndham uses to describe her family and their holiday traditions of homemade decorations, ``sprinkle'' cookies and festive gatherings. This Christmas season, however, promises to be different, with the anticipated arrival of a sophisticated young guest whose mother was once Mrs. Wyndham's best friend. Both intimidated and impressed by Deirdre Frances, a native New Yorker her own age, Till regards her new acquaintance as a status symbol and uses her to impress her schoolmates. Only when she recognizes Deirdre's anger and vulnerability can Till view the girl as an equal and begin to build a real friendship. This perceptive first novel stars a high-spirited protagonist with a lively imagination; her problems with family, peers and self-image are sensitively related. Although some of the book's transitions are less than smooth, Thacker ( Summer Stories ) clearly conveys universal preteen concerns while inducing a good many chuckles. Ages 8-12. (Oct.)