The number of children beginning public school in the United States who speak Spanish as their native language--Spanish-speaking kindergartners (SSK)--continues to increase. It is important that the teacher workforce acquire the characteristics and the instructional and curricular tools necessary to provide these children with meaningful early educational experiences so they can succeed academically. This article focuses on a recent study that used data from a nationally representative sample to find that teachers' use of Spanish in the classroom has a small effect on the mathematics achievement of SSK, such that Spanish use was associated with higher scores. Two hypotheses are offered to explain why the prevalence and size of this effect was found to vary by the following sociodemographic conditions (i.e., levels of human capital in the home): socioeconomic status, parent education, and student level of English proficiency. Limitations to this study and implications for future research are discussed.