Understanding the cognitive underpinnings of children's arithmetic development has great theoretical and educational importance. Recent research suggests symbolic and nonsymbolic representations of number influence arithmetic development before and after school entry. We assessed nonverbal ability and general language skills as well as nonsymbolic (numerosity) and symbolic (numeral) comparison skills, counting, and Arabic numeral knowledge (numeral reading, writing, and identification) in preschool children (4 years of age). At 6 years of age, we reassessed nonsymbolic (numerosity) and symbolic (numeral) comparison and arithmetic. A latent variable path model showed that Arabic numeral knowledge (defined by numeral reading, writing, and identification at 4 years of age) was the sole unique predictor of arithmetic at 6 years. We conclude that knowledge of the association between spoken and Arabic numerals is one critical foundation for the development of formal arithmetic.