Research Findings: The current study aimed to explore the independent and interactive roles of individual student-teacher relationship quality and classroom-level self-regulatory supports in kindergarten for children's self-regulatory skills in kindergarten and first grade. We did so using multiple measures of children's self-regulation, drawn from multiple sources, and a relatively new measure of classroom-level supports for self-regulation. Our sample included 726 low-income kindergartners in Tulsa, Oklahoma. Controlling for children's fall of kindergarten self-regulatory skills, student-teacher relationship quality in kindergarten was associated with children's self-regulation at the spring of kindergarten and again at the fall of first grade, but classroom-level self-regulatory supports in kindergarten were never significantly associated with children's self-regulation. Overall, associations between student-teacher relationships and children's self-regulation were stronger and more consistently significant for student-teacher conflict than closeness, and for teacher-reported than directly assessed or assessor-rated self-regulation. They did not, however, vary by classroom self-regulatory supports. Practices and Policy: Results affirm the primacy of student-teacher relationships for children's self-regulatory development across the transition into formal schooling, regardless of the quality of classroom-level supports for self-regulation. Teacher training and professional development programs should equip teachers with strategies and resources that support their ability to develop warm, responsive relationships with individual students.