The Cartilla para enseñar a leer (1569), attributed to Flemish Franciscan Pedro de Gante, was one of the most important primers from the early years of the viceroyalty of New Spain. Nevertheless, the primer's importance during the process of cultural contact has been largely ignored. As did other primers of the period, the Cartilla contained the most important prayers, but what sets the Cartilla aside is that its selection of prayers is presented in a trilingual version, in Castilian, Latin, and Nahuatl. The content of the Cartilla invites the question as to why Gante, a missionary focused on writing doctrinal works in Nahuatl, would compose a primer that is trilingual, but raises another that is perhaps more perplexing: Why were most of the prayers in Castilian? In this article, I intend to shed a light on Gante's decision to create a complex tool that could be employed by a mixed audience of Castilian, creole, mestizo and Nahua children. By doing this, Gante unwittingly started a process of cultural contact in which language played a pivotal role. The Cartilla thus presents itself as a multifaceted tool that helped shaped the culture of the Basin of Mexico during the early years of the viceroyalty.