The relationship between basic oral language and early numeracy has been studied extensively, but results hardly include kindergartners' math language, which might mediate this relationship. The aim of this study was to investigate the development of basic language skills--specifically, math language and low early numeracy. Dutch children (4-5 years old; N = 1,030) were screened for having low early numeracy skills, and low performers (n = 199) were followed for 2 years and tested four times throughout kindergarten. The development of general language skills and early numeracy were investigated with latent growth modeling, revealing a significant mutual relationship. Further, the relationship between basic language and early numeracy was mediated by kindergartners' specific math language, suggesting that specific math language has a key role in the early numeracy learning process.