It's a truism that writers, like musicians, must practice their scales before they take flight. Are the practice lessons themselves of any literary value? Rarely, judging from these two volumes, other than as scholarly footnotes--although Jane Austen's The History of England, composed in 1791, when the future author of Pride and Prejudice was only 16, proves a happy exception. Though the 60-page manuscript has appeared previously in Austen collections (most recently in Oxford University Press's Catharine and Other Writings, 1993), it's never before been published in facsimile--an important point since Austen's handwritten manuscript was accompanied by profuse color portraits drawn by the writer's older sister, Cassandra, reproduced here. Intended to burlesque Oliver Goldsmith's wildly popular, four-volume The History of England from the Earliest Times to the Death of George II, Austen's little book, as A.S. Byatt points out in an introduction, displays ``an unusual mixture of lively energy and gleefully confident control''--as witnessed by this opening sentence to Austen's brief life of Henry V: ``This Prince after he succeeded to the throne/grew quite reformed and amiable, forsaking all his dissipated Companions, & never thrashing Sir William again.'' That sort of dry, sophisticated wit abounds throughout, making this an esoteric pleasure. Generally less involving are most of the bits of juvenilia excavated by Paul Mandelbaum, a freelance journalist, in First Words. Arranged alphabetically by their 42 authors, from Isaac Asimov to Tobias Wolff, the entries include such items as Jill McCorkle's short-short ``The Night Santa Failed to Come,'' written when she was seven; eight-year-old Amy Tan's essay, ``What the Library Means to Me,'' and--far more polished--a long mystery story (``Untitled Mystery'') from 14-year-old John Updike. The collection makes clear that, even when very young, many writers work with ideas that will hallmark their adult work (e.g., Stephen King at age nine writing in ``Jhonathan and the Witchs'' [sic] of a quest confounded by supernatural evil), and Mandelbaum does an energetic job of pointing out, in introductions and sidebars, thematic relations between each author's older and newer writings--though his comments do sometimes sound almost tongue-in-cheek: ``The childhood piece that follows is precocious in its prose and is an early foray in [the author's] ongoing exploration of masculine terrain but doesn't quite anticipate his roles as literary philosopher and cultural provocateur''--this pronouncement applied to ten-year-old Norman Mailer's ``adventure epic,'' ``The Martian Invasion.'' Still, Mandelbaum's collection has a certain novelty interest and, for manic completists, it no doubt will prove a must.