Research Findings: The objective of this study was to examine the student-teacher relationship as a potential moderator of the link between executive functioning (EF) and children's early school readiness among a clinical sample of preschoolers with externalizing behavior problems (EBP). Participants for the study included 139 preschool children (75.54% boys, "M" age = 5.01 years, 84.94% Hispanic/Latino) with at-risk or clinically elevated levels of EBP. The student-teacher relationship was assessed using the Student-Teacher Relationship Scale. School readiness data were composed of standardized achievement test scores and teacher reports of kindergarten readiness. EF was measured via parent and teacher reports along with standardized measures of EF, including the Head-Toes-Knees-Shoulders task and 4 standardized subtests from the Automated Working Memory Assessment. Poorer student-teacher relationship quality was predictive of lower teacher-reported kindergarten readiness and higher academic impairment. Main effects were qualified by an interaction between EF and student-teacher relationship quality such that worse EF (parent/teacher reports and standardized performance) was only associated with lower teacher-rated kindergarten readiness for children with poorer student-teacher relationship quality. Practice or Policy: EF appears to be an important predictor of school readiness for preschool children with EBP, particularly for children experiencing poorer student-teacher relationships.