Lawrence, KS Lexical acquisition occurs rapidly and with relative ease in typically developing children. Children can form an initial representation of a novel word following only a single exposure (eg, Dollaghan, 1985). The number of root words known increases fromapproximately 3,500 at thebeginning of kinder-garten to about 6,000 at theend of second grade (Biemiller, 2001; Biemiller & Slonin, 2001).

While there is clear evidence that children learn words rap-idly, what remains to be discovered is how children are able to accomplish this complex task so effortlessly. To learn a word, a child must storein memory two types of representations-se-mantic and word form-as well as the links between them (see Gupta, this issue). The semantic representation refers to the mean-ingful information regarding a referent (eg," a toothed strip of rigid material for arranging the hair" for" comb"). A wordform representation refers to the combination of sounds as a whole sequence and constitutes the word form (eg,/koUm/for