This study examines the effect of an intervention called Native Numbers on the development of number sense and quantitative skills in low-SES preschool children (ages 5 to 6) in Mexico City, using a randomized control trial (RCT). Native Numbers (NN) is a math curriculum built as an application for "iPads" that includes activities on number concepts, relations, ordering and counting. The study was conducted in 2014, with eight participating schools and an analytic sample of 249 students. The intervention lasted two weeks in each school, and compared students randomly assigned to a group using NN with a group using "iPads" with no educational content. Data was collected on pre and post measures of student's cognitive skills, as well as contextual information from families. This study shows a small potential positive effect of "Native Numbers" on quantitative abilities of children, though there is a lack of statistical power to find significant effects. However, heterogeneous effects of the treatment were found for mothers' schooling. A statistically significant interaction between treatment and mother's years of education revealed that the impact of the treatment was significantly higher for children whose mothers had fewer years of education. The frequency of home numeracy activities was also statistically significant in this model. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]