Sometimes, at an advanced level of teaching, these kinds of 'interventions' are pre-planned by teachers to put two sides of a question. Students love it. Unpla

Sometimes, at an advanced level of teaching, these kinds of 'interventions' are pre-planned by teachers to put two sides of a question. Students love it. Unplanned interventions can make it harder to present hard ideas. Quite often in maths you have to present hard stuff as a process of 'diminishing deception' or as a move from concrete things in the world through procedural routines to abstract concepts, see http://homepages.warwick.ac.uk/staff/David.Tall/themes/how-humans-think-mathematically.html http://homepages.warwick.ac.uk/staff/David.Tall/themes/how-h... and the sample Chapter 1 for one model of that process. I'd imagine a colleague who has a different way of unwinding the ideas jumping in part way through a presentation like that might reduce the clarity of the presentation. Just wondering...