One of the main challenges of MOOCs is effectively facilitating learners in the course forum, especially as participation grows. Teaching assistants (TAs) can help, but their instructional approaches and effectiveness in promoting learning are questioned. This study examines TAs' instructional methods in two MOOCs using mixed methods, evaluating their facilitation strategies against a widely accepted MOOC instructional quality framework. Content analysis, interviews, and linguistic and social network analysis reveal that TAs often provided direct answers rather than fostering problem-solving and collaboration. The findings suggest design implications for developing tools to assess and improve TAs' instructional approaches, providing feedback to enhance online course design and support.