This study explored the development of Ecuadorian Kindergartners' spontaneous focusing on numerosity (SFON) during the kindergarten year, as well as the contribution of early numerical abilities to this development. One hundred Kindergartners coming from ten classrooms received two SFON tasks, one at the beginning and one at the end of the school year, and an early numerical abilities achievement test at the beginning of the school year. Results first demonstrated limited SFON development during the kindergarten year, with inter-individual differences and intra-individual stability of children's SFON tendency. Second, both children's SFON tendency and their early numerical abilities at the start of the kindergarten year were predictively related to their SFON tendency at the end of the year. Our results do not only add to our theoretical understanding of SFON in young children, but also inform educational policy and practices in the domain of early mathematics education in Ecuador, as they provide building blocks for optimizing the educational goals and curricula for kindergarten mathematics.