Teacher facilitation of CSCL activities is widely recognized as one of the main factors affecting student learning outcomes in formal face-to-face settings. However, the orchestration load that such facilitation represents for the teacher, within the constraints of an authentic classroom, remains under-researched. This paper presents a novel method to estimate the cognitive load of teachers during facilitation of CSCL sessions, using mobile eye-tracking techniques. Throughout three studies of increasing authenticity, we demonstrate the feasibility of this approach, and extract insights about classroom usability challenges in CSCL practice: the increased load of class-level facilitation, or the real-time monitoring of students’ progress. This new instrument in the CSCL researcher’s toolkit can help focus our attention in critical, fine-grained classroom usability episodes, to make more informed design decisions.