<p>Collaborative problem solving (CPS) and mathematical reasoning are both crucial twenty-first-century competencies. Research suggests that aspects of CPS can benefit mathematics learning. At the same time, particularly in disciplinary settings, successful CPS may require facilitator support alongside students’ social and cognitive skills. This sequential explanatory mixed-methods study investigates the impacts of human facilitation on supporting CPS during online small-team collaboration in mathematics. Using learning analytics techniques such as epistemic network analysis and sequential pattern mining, we analyzed and compared chat logs from human facilitated and unfacilitated teams in high school classrooms. This quantitative analysis identified frequent sequences of facilitator moves and CPS behaviors, as well as sequences of CPS behaviors distinguishing human facilitated and unfacilitated chats. We then analyzed chat episodes featuring these sequences for the role of facilitation in mathematical problem-solving processes. Results indicated that human facilitation effectively promoted constructive behaviors such as multiple turns of social negotiation, while reducing inappropriate communication. Different facilitation strategies, such as soliciting disagreement or negotiation, elicited targeted CPS behaviors and promoted mathematical reasoning and explanation, likely contributing to improvements in team performance. Findings have practical implications for facilitating CPS in CSCL mathematics settings.</p>