Evaluation
How participants give feedback
Feedback from participants is the most direct way to know whether the session did what you designed it to do.
Evaluation means collecting participants' experience of the session: what worked, what did not, what they took away, and how they would rate it. That feedback is what separates a facilitator who gets better over time from one who runs the same session for years and never finds out why it always feels slightly off after the lunch break.
The hard part online is timing. If you ask for feedback at the end of a call, most people have already closed the window by the time you finish your closing sentence. Getting evaluation to actually happen requires planning it in, not hoping for it.