In a controlled study, teacher-researchers investigated pausing during lectures. In a 50-minute lecture, the instructor paused every 12-18 minutes, 2 minutes each time, and students were directed to share their notes with their neighbors so they could fill in missed information or answer questions for each other. The instructor left 3 minutes at the end for students to write down everything they could remember from the lecture at that time. Students who had the pausing treatment did significantly better on both the free recall at the end of the lecture and on a 65-item test, 12 days later, than students who received the same lectures without pausing.My own experience corroborates these findings. I've made a concerted effort over the years to break up lectures into smaller chunks and insert opportunities for students to review and ask questions. Sometimes I'll guide this effort a little bit by giving the students a simple writing prompt to stimulate reflection or synthesis on the lecture material. I don't have any systematic data of my own, but I do notice that the questions students ask post-pause tend to be better than those that 'interrupt' the lecture: more probing, more thoughtful, more summative. So there's definitely something to be gained just by letting students catch their breaths in lecture.
Lectures are a very efficient way to expose students to a lot of information in a short period of time, but lectures lose their efficiency if students can’t take effective notes or can’t remember what they heard. Pausing the lecture and directing students in an activity to help them process the information right then and there will help them brush up their notes and establish the material in their minds. Pausing is, itself, very efficient – only 6 minutes of pausing during a 50-minute lecture produced significant improvement in student retention of material.
(The study mentioned above: Ruhl, K., C. Hughes, and P. Schloss. 1987. Using the pause procedure to enhance lecture recall. Teacher Education and Special Education 10: 14-18.)