Numerical comparison is a primary measure of the acuity of children's approximate number system. Approximate number system acuity is associated with key developmental outcomes such as symbolic number skill, standardized test scores, and even employment outcomes (Halberda, Mazzocco, & Feigenson, 2008; Parsons & Bynner, 1997). We examined the relation between children's performance on the numerical comparison task and the number-line estimation task. It is important to characterize the relation between tasks to develop mathematics interventions that lead to transfer across tasks. We found that number-line performance was significantly predicted by nonsymbolic comparison performance for participants ranging in age from 5 to 8 years. We also evaluated, using a computational model, whether the relation between the 2 tasks could be adequately explained based on known neural correlates of number perception. Data from humans and nonhuman primates characterized neural activity corresponding to the perception of numerosities. Results of behavioral experimentation and computational modeling suggested that though neural coding of numbers predicted a correlation in participants' performance on the 2 tasks, it could not account for all the variability in the human data. This finding was interpreted as being consistent with accounts of number-line estimation in which number-line estimation does not rely solely on participants' numerical perception.