In the first decades of the twentieth century, amidst the emergence of experimental psychology, Latin American educators became pedagogical innovators and advocates of school reforms. They used the classroom as a laboratory to study children's intelligence and collect data that could potentially improve their education. This paper traces laboratory practices in Argentina and Brazil developed by women between the 1900s and 1920s. In Argentina, we investigate the work of Víctor Mercante's mentees at the Universidad Nacional de La Plata. In Brazil, we explore the laboratory of the "Liga Brasileira de Higiene Mental," especially the work of normalist teacher Maria Brasília Leme Lopes. Drawing from scientific journals, teachers' memoirs, and newspapers, we argue that women were crucial actors in the development of experimental psychology in these countries. We highlight the laboratory practices that women carried out in an attempt to understand children's minds to better educate them. Yet, we also show that the effects of experimental psychology in the classroom had a negative impact on children's educational experience. Looking at Latin American women educators contributes to expanding the spaces and actors in the history of experimental psychology in connection with pedagogical reforms. By paying attention to less explored geographies of knowledge-making such as South America, and the classroom as the laboratories where scientific practices developed, we position Latin American women in dialogue with scientists and school reformers in Europe and the United States.