This project is identifying cognitive and neural mechanisms by which early numerical learning occurs and using this knowledge to improve numerical skills in children before entering school. In addition, it is developing and empirically validating a methodological framework for enhancing early numerical development. Building on work previously conducted with NSF support, the investigator is conducting a full-scale, randomized, experimental training study of the effectiveness of five different PC-based, in-home training interventions on numeracy in pre-school children. The study has a mixed cross-sectional and longitudinal research design that will yield both correlational and causal (quasi-experimental, experimental) evidence.