This study explored factors that are associated with calculation development among 176 children at-risk for learning difficulties. Data were collected on working memory, language, non-verbal reasoning, processing speed, decoding, numerical competence, incoming calculation, SES, and gender at the beginning of 1st grade and on calculations over 4 time points (from 1st grade to 3rd grade). Latent growth model analysis showed that numerical competence, processing speed, decoding, and incoming calculation significantly explained the variance of calculations at the beginning of first grade. Early numerical competence, in particular, predicted the calculation development from the beginning of 1st grade to the end of 3rd grade. Implications of findings regarding to early calculation instructions for at-risk children were discussed.