If an instructor is lectern-bound, she will have greater proximity to students near the lectern. Equitability requires mobility. Group work also helps. It typically places students in different parts of the room and we typically stroll about in monitoring groups' progress. I believe it's five to six feet, near to touching distance.
Research finds otherwise.
An obviously needy student captures a teacher's attention, but if the student is not obviously needy, we tend to direct attention to students perceived to be particularly engaged. Attentive Listening Attentive listening refers to the use of our demeanor to focus on a student's comments or questions. It is easy for us to devote less than our full attention to a student, especially one we see as less able, even though we want nothing more than to have an interactive classroom. We tend to devote fuller attention to students we perceive as particularly able. Some of us are prone to engage in personal conversations, before or after class, with some students but not others.