We assessed a range of theoretically critical predictors (numerosity discrimination, number knowledge, counting, language, executive function and finger gnosis) of early arithmetic development in a large unselected sample of 569 children at school entry. Assessments were repeated 12 months later. Although all predictors (except finger gnosis) were moderate to strong correlates of arithmetic, a latent variable path model showed that only number knowledge and numerosity discrimination were unique predictors of arithmetic development over the 1st year of formal education. These findings are consistent with the Triple Code Model (Dehaene & Cohen, 1995) suggesting that both nonsymbolic representations of numerosity and visual symbolic representations of number are critical for the development of arithmetic. Our results suggest that the assessment of numerosity judgments and Arabic number knowledge at school entry may be useful for identifying children at risk of difficulties in acquiring arithmetic skills.