Mentors' feedback can assist preservice teachers' development; yet feedback tends to be variable from one mentor to the next. What do mentors observe for providing feedback? In this study, 24 mentors observed a final-year preservice teacher through a professionally video-recorded lesson and provided written notes for feedback. They observed the lesson for a second time and focused their feedback on the preservice teacher's questioning only. Findings showed that the mentors' written feedback varied considerably when open observations occurred. However, there were fewer items when they focused on one teaching practice (i.e. questioning), which also provided a deeper analysis of this specific practice. Research is required around the dimensions of observations (i.e. visual, auditory and conceptual), observations of specific practices, and methodological approaches for observing and collecting data about a preservice teacher's practice.