Experiences of poverty and racism in early childhood can overburden physiological systems that respond to stress with implications for the development of the prefrontal cortex and related executive functioning. The present study is unique in its examination of basal cortisol output across the preschool day in relation to teacher ratings of executive functioning. Participants were 310 children attending Head Start preschool in the United States, a majority of whom were Black, Hispanic, or Asian Heritage. Salivary cortisol was sampled in duplicate at 4 times across 2 days near the beginning of the school year, resulting in a total of 16 samples per child. Several weeks later, the BRIEF-P teacher rating scale assessed various components of executive functioning. (author abstract)