The purpose of this study was to examine possible correlations between collaborative action-taking and instructional practices supportive of student Social-Emotional Learning (SEL) among U.S. lower secondary-level teachers. This quantitative, ex post facto study utilized existing data from the 2018 Teaching and Learning International Survey (TALIS), sponsored by the Organization for Economic Cooperation and Development (OECD). Descriptive analyses provided a snapshot of current collaborative action-taking and instructional practices supportive of SEL across U.S. schools among lower secondary teachers (grades 7-9). Correlational analyses identified the relationships between the independent variables, types of teacher collaborative action-taking, and the dependent variables, specific instructional practices known to be supportive of SEL. Based on a review of literature related to educator collaboration and SEL and an analysis of the gaps and potential intersections among these phenomena, the study hypothesized that there would be stronger associations between higher-level, more interdependent collaborative actions (where teacher interactions are substantive and sustained) and SEL-supportive instructional practices. Results showed that while U.S. lower secondary teachers reported frequent engagement in lower-level “exchange” collaborative actions, they reported less frequent engagement in higher-level, more interdependent collaborative actions. Regarding SEL-supportive instructional practices (operationalized using Li and Julian’s 2012 Developmental Relationships framework), teachers reported more frequent engagement in practices linked to the framework’s element of expressing care and less frequent engagement in practices linked to the elements of providing support and challenge and expanding possibilities. Results of correlational analyses showed strong, statistically significant relationships between frequency of engagement in higher-level collaborative actions and frequency of enactment of specified SEL-supportive instructional practices. However, the hypothesized stronger relationships with higher-level collaborative actions were present in some, but not all, of the expected cross-tabulations with SEL-supportive practices. Findings from this study are interpreted to inform their implications for emerging understanding of the pathways and barriers to effective, equitable SEL in P-12 schools.