Background: A number of contrasting hypotheses have been put forward concerning mathematical performance deficits in children with specific language impairment (SLI). However, debate as to the nature of this deficit continues. 'The present study analyzed whether the trajectories of SLI-children may be attributed to the use of symbolic vs. linguistic assessment tasks, or to a deficit in the magnitude system. Method: SLI-children (N=20) and typically achieving children (N=20) were monitored between kindergarten and first grade. Four tasks were designed, each with varying demands on language, symbolic, and domain-specific skills. Results: The groups only differed in the trajectories of those numerical tasks involving high language demand. Conclusions: These findings indicate that SLI children present an early deficit in the development of numerical skills that require retrieval from long term memory and articulation of a phonological representation. Number skills involving greater language demand should be included as part of SLI early detection and intervention protocols.