Contributions of longitudinal studies to evolving definitions and knowledge of developmental dyscalculia

In the last 20 years, longitudinal studies have demonstrated that it is important to attend to the stability of mathematical performance over time as a facet of dyscalculia, that the manifestation of mathematics difficulties changes with development, and that individual differences in cognitive profiles and learning trajectories observed in children with mathematics difficulties implicate differences between dyscalculic and non-dyscalculic subgroups. Intra-individual differences over time, and external factors related to children's learning environments, also contribute to performance trajectories; moreover, these factors may explain the inconsistent performance profiles observed among many students whose difficulty with mathematics emerges later or diminishes over time. Longitudinal studies on DD are also an important tool to elucidate why some children are more responsive to mathematics intervention than others.