This case study describes a longitudinal study of children’s social-emotional development. The project was a mutually beneficial collaborative effort between the researchers and a preschool program for low-income families located in a multicultural community in the Northwest United States. We encountered several challenges in implementing the study. At the time the project was implemented, there existed no readily available measures of emotional development with proven reliability and validity for use with preschoolers. This problem was exacerbated by the fact that multiple languages were spoken by the children at the preschool; thus, any measure we used would need to be translated and proven psychometrically sound in different language versions. The study also extended over several years and involved conducting thousands of individual assessments with the preschoolers. In this case study, we describe how those challenges were managed and how we ultimately were able to provide useful information to the program about their students’ social-emotional development. In addition, we describe how the data collected allowed us to investigate fundamental questions about emotional understanding development across the preschool years, as well as how emotion understanding affects and is affected by other aspects of social development. Throughout the process, we learned much about emotional development, different analytic techniques, as well as methods for dealing with the challenges associated with community-based and longitudinal research.